@dr_stratcat I’m not sure if I completely understood your problem, but I feel that it might help you to train finger independence. I made up some (bassless) exercises for that.
I start by touching each finger with the thumb on both hands simultanously up and down:
L: index - middle - ring - pinky - pinky - ring - middle - index
R: index - middle - ring - pinky - pinky - ring - middle - index
repeat as many times as you want, but stay relaxed
Then change it up by starting on index with the left hand and pinky on the right hand
L: index - middle - ring - pinky - pinky - ring - middle - index
R: pinky - ring - middle - index - index - middle - ring - pinky
It takes a whole lot of concentration on the first few tries, but it gets better quickly. It helped me to hold up my hands in front of my face with both palms towards my face and just thinking left to right to left to right.
Next level would be taking three steps:
L: index - middle - ring - middle - ring - pinky - pinky - ring - middle - ring - middle - index
R: index - middle - ring - middle - ring - pinky - pinky - ring - middle - ring - middle - index
Then change it up again by starting on index with the left hand and pinky on the right hand
L: index - middle - ring - middle - ring - pinky - pinky - ring - middle - ring - middle - index
R: pinky - ring - middle - ring - middle - index - index - middle - ring - middle - ring - pinky -
Third level would be skipping one finger, just like this:
L: index - ring - middle - pinky - pinky - middle - ring - index
R: index - ring - middle - pinky - pinky - middle - ring - index
Flip it over to:
L: index - ring - middle - pinky - pinky - middle - ring - index
R: pinky - middle - ring - index - index - ring - middle - pinky
Hope this helps