Technically speaking, only playing all chapters could be considered an Any% version, so I'm a bit confused. Is there a way to skip some chapters?
Yes in Any% you mostly skip chapters
How? Is there some sort of glitch? Or is there just something that's blatantly obvious that I never noticed? What chapters can you actually skip?
Also, unrelated question, but what do you do when the game crashes mid-run? I've experienced numerous crashes during a simple casual playthrough, so is this a common issue?
I recommend you watch a Any% speedrun to see for yourself. And if I am not mistaken if your game crashes you just continue where you left off, someone correct me if I am wrong
If your game crashes, you can continue (if you didn't select continue without saving), but the timer must continue while you re-enter the file after the crash.
Also, for any% there is an out of bounds trigger to the final level, which you can reach and beat the level (using several glitches). This technically doesn't finish the story, but it has been recognised as the end of the game for the purposes of any%.