@Mac When I’m learning a piece, I break it down into bite size morsels and learn them one at a time. The morsels might be a bar or two, or an entire phrase. When I come across a difficult part, I will work on that in isolation until I get it, and then join it with the other parts before and after.
That’s just me, and how I like to do it. YMMV.
And don’t apologize for using tab, it’s better than not playing at all until you master reading notation.
I’m still in the middle of B2B so this answer is coming from the piano player part of my brain. It depends how hard it is. I’ll make a choice if it’s within reasonable reach or just too far beyond my edge to attempt just yet. Either way, I’ll simplify it down to something I can play and play through it that way a few times first. I’ll make sure I hit the critical framework of the chord changes and cleanly hit the 1 if nothing else. Then I may try to work on just the rhythm of the complex part either saying the rhythm or playing it on one note. (Saying the rhythm seems too easy and silly, but strangely it wires up something in the brain that translates to moving the fingers) If I can’t get it all I may play half as many notes as are written or leave out the really strange move. That’s enough for me to have fun with the song and still be working on my skills. If I’m going to try for the whole thing I run just the really strange move over and over to work on that muscle skill and then try to put it together at a slow speed.
Only right answer is your answer… All of us have different personalities which means we all have different triggers that drive us. For some, skipping works best… For others, pushing through to the end works best…
For me, pushing through is what I like to do because that just happens to be who I am… Doesn’t mean that THAT is the only way, but even though, there have been times when I’ve had to back down and move on in order to keep moving forward. Only you can make that call. It’s not like you’re quitting or anything… it’s just a temporary roadblock that you might need to come back to later on.
When you’re learning a new song, there will probably be something new that needs to be learned - it’s all part of the fun of learning and playing music… Challenges help feed the passion to play - passion helps challenge abilities… Only you know the limits that challenge you based on your passion…
Keep on Thumpin’!
Lanny
Thanks @Lanny
I was always of the mind “ dig deep and throw well back “ which has led me to a few ups and downs in life but generally served me well.
I’m really trying to use my playing time as a way to relax but something drives me . At every opportunity I have my bass in my hands .
Strange but true
There ain’t no hills when you’re a ‘High-Stepper’ @Mac…
Keep on Thumpin’!
Lanny
There’s a certain mountain I personally decided on that it is just too damn high and steep for me and will be for quite a while still.
That doesn’t keep me from looking up that mountain from time to time. But I can’t even get a hold for the first step up that mountain right now.
It’s not meant as whining. I am just saying it is also okay to have long distance goals.
Many thanks @Lanny
You are far from a whiner @juli0r
From my short time here I see you as a highly intelligent and articulate fellow.
It is perfectly possible to whine intelligently and articulately, so the two are not mutually exclusive. 
Skip the section, but don’t skip playing. Stay consistent but find something else to play or alternate material to learn.
Great question, with many excellent suggestions, and points of view, and gotta love the support and encouragement from all.
All advice so far has been excellent, but not all advice will be what’s right for you. This is where you have to filter some of it, and use what is best for you.
We all learn different, we are individuals with different brain chemistry, so you will be best following the things that suit you best.
For instance, some can read something and do it, but struggle trying to copy what others do, and others can’t make things work after reading about it, but put them with a person that shows them one time in action, and off they go.
All that said, here is my bit.
This was a huge thing for me starting bass a few months back.
When I was young and started playing guitar, I wanted to learn all my favorite songs. Of course, they were way beyond what I could learn, self teaching along the way.
I was great at nailing the main riffs, and intro riffs, some rhythm stuff.
I could play all the song riffs and rhythms to impress, but I could not play one song all the way thru.
Then I started playing in a band, 2nd guitar, and learned all the songs we wanted to play, a dozen or so. Then we wrote 5 or 6 of our own, a couple parody songs, and that’s about it.
My best friend, the bassist, always poked fun at me for not learning the whole song.
I was going, having a blast coming up in life, in love with partying and my future X wife, starting a career, and playing enough to be content, sort of. It did leave me a bit unsatisfied, and lacking confidence, but I had no time to sacrifice for lessons to help me breakdown the part of reading tabs thru full songs, and learning rhythm and tempo, or practicing enuf, or doing finger exercises or many things that could have made me a better player, or things that may have kept me playing still, who knows, but I think ultimately, I stopped playing because of frustration, not being to progress past learning the next hit riffs in the monthly guitar magazine.
That and my life getting more structured and complicated as I got older.
So, here we are, I have taken a totally different approach to picking up bass. I started with a basic learn bass book with basic instruction, and simple open string pluck lessons,mfretting, some note names, scale shapes, etc… Got into scale shapes, knew I needed more then a book, so I went online. Started watching all the YT vids, bounced around free lessons, and started landing on a couple websites from different YT channels.
You guys know how it went, you have all done it, but I remained focused, (and still sort of do) on learning the bass, and music theory to help with bass.
I refrained from funning out and learning every song I want to learn on bass.
I ended up at SBL, going thru the free courses. They were fine until from one lesson to the next, it got, “wait? Wtf? How am I supposed to follow this, you never taught 90% of what you are teaching.
So I left for more basic instruction. Looked at Talkingbass, The bass Wiz and here, and here is where I got.
I still feel it’s important to learn the bass, but we have to play music too, and have fun.
I learn a few songs here n there, and yes I know riffs to a lot of songs (many remember from guitar) and I have fun, but I have only stuck to a couple songs, to learn all the way thru, every last note, and I am almost there.
But, one of them, I had / have instructor guidance, I never would have gotten it from tabs, and got pretty far with a YT vids, but it still took a teacher for me to get it.
The other song is long, and lots of bass changes in it, with a great bass intro., but one I am doing with play along with tabs, and, not there yet, but I can get there with what I have learned already.
The point is, some things in difficult songs, I am not ready for. It’s not to say that I couldn’t sit there for ever, focusing on only this song and it’s parts, but my time may be spent better learning more about bass and music itself, and then when I know this, if I go back to that song, I am ready and can tackle that challenge more readily.
So, when faced with this song, I could play the notes, but couldn’t get the timing right without cheating. I was not prepared for this song because I never learned 16th note syncopation.
So, working with my teacher, and learning how to practice the notes and syncopation I never learned, I was able to get the song right, and learned something that will help me grow musically.
The next song was this exactly…
I did this 2 bars at a time, then put 2 sets of two together, and continued til I got the intro down.
I know the main riff well, but its a 6 min song, with about 3 more minutes I need to learn, 2-4 bars at a time. But I have the skills to do this. It’s a challenge, but of a different kind. I have work to do, but work I am ready for.
All I am saying is, if this is stuff you know, and you just need to memorize it, or practice moving up and down the fretboard rapidly, stick to it, you will get it.
If it is past a level that you have learned this far, possibly learn what it is you have not learned. Is it timing, is it technique, is it finger strength?
Make this a lesson, so the time you spend learning the song helps you grow musically.
It’s the beauty in Josh’s B2B, he taught us to play music, related to the lesson he was teaching us, so that the song itself helps you grow musically.
I used to play some pretty fast, difficult parts in speed metal songs on guitar, but I learned only the song, not the lesson the song could have taught me if I looked it at it from that other direction.
There is no wrong answer here if you are satisfied with the result, as I was back then. But I would not be today, because I did not grow musically.
There is no shame in putting it aside, and if you want to play full songs right now, choosing one that you have the tools to be able to tackle.
Today I wanted to do something new. I wanted a small break from these two songs. I scrolled across a song. I said, that’s perfect. I know the song. I knew the riff on guitar. The bass is similar, but different. It’s a lot of right hand chugging, it ha fret hand, not too hard, and I had one requirement for a song to learn today…
Had to be something I could play without using my left thumb. I shouldn’t be playing at all, but I can’t not🤔
So, 95%. I can do without the thumb, so I played it.
Intro 2 bars, 3 parts 4 bars each, played
Intro - 2x
Part 1 - 2x
Part 2 - 2x
Part 1 - 2x
Part 3 - 2x
Part 1 - 12x
Part 2 - 2x
Part 1 - 4x
So, I had the ability to play the parts, I practiced each for a bit, and then started playing to the song.
That was about 3 hours today.
Left me feeling great.
I played a song all the way thru, that’s not how I used to do things, and it’s how I want to do things now.
I played today and still rested my thumb.
And O rocket the F out
Paranoid by Black Sabbath
The other 2 songs I am talking about, one is slap, that one took help from Josh.
Take the power back - RATM
And
NIB - Black Sabbath.
Nib intro is down. The main riff is down. I am starting to bite size his bass play that gets a bit intense, nut it’s in my wheelhouse.
RATM,I still have one fill, with the timing I can’t yet master, but I can play it thru 90% otherwise at this time.
I work on both still, along with regular practice
HTH you think about which advice works best for you. I can’t tell you do it like I do, cuz I don’t know you like you know you. I am sure you will work it out in your best way, and as long as you stay happy when your bass is in your hands, that’s the measure that tells you are doing a good job, and doing it right.
Great reply @T_dub as have all the others been.
They have all given me different perspectives on the subject and yet in many ways have the same or very similar message “ if it’s fun you’re doing it right “.
I’ve taken a lot away from the replies and thank you all 
Sounds like we have about the same background with guitar and bass and about the same approach to learning now on bass. Great advice.