Hey Jean! Thumb plucking is cool for some of the purposes listed in this thread - chords in particular - but I very very strongly recommend sticking to index-middle alternating for the course.
Otherwise you end up using the thumb as a crutch to avoid alternating weaknesses, which means more problems later on.
Like @Ant 's example above, I’d recommend against the thumb on that, because the thumb is more soft and fleshy, so those plucks won’t hit the same way the index/middle plucks do, and it creates inconsistency.
So yeah, I basically only use it in these cases, none of which are standard:
- if I want soft thumb-y plucks
- chords
- palm mutey thing
Unless you’re doing an insane thumb-index-middle-ring shred technique like that video @Wombat-metal metal linked of course! But you’re gonna need high gain / distortion / super bright tone to make up for the softer plucking.