Do they just mess around? Do they know the code very well? It’s always been something that interested me (along with a TAS, but I’m pretty sure that's not going to happen). But I’m not sure how people actually discover new glitches, is there a process or something?

usually they use modzone 2 which shows alot of hidden content like behind black screens, hitboxes, movement values, etc... and try a bunch of stuffs with theories made out what modzone 2 has.

Or they just... play the game, like me who found (known) rare glitches and one of them seems to be unknown. However i still think its rare to find new glitches with so many glitch hunters from years ago and with modzone 2

just basic understanding of the game