>Why do my drawings look "unpolished"?
I don't know, post an example



>but the lines like hair and borders etc… Am I missing something? I remember watching a drawing livestream and the artist used some kind of dynamic brush/tool that would automatically clean up each stroke and line they sketched, even curved ones.

So you have issues with outlines?
Trace
No, really
Set a white mask with 50% opacity and trace the lines
You can erase taper the edges, that's fine.
Don't do the scratchy shit. Trace those sections whole.
Don't bother with smart tools for now. Learning to do clean lines will help your precision on every single front.
A strong base helps several orders of magnitude more than any niche trick.