Hi,
I've been using an alternate java version then the one packaged with minecraft as I found it tends to run better with the large amounts of mods I have normally - AdoptOpenJDK - and for some reason, this mod crashes instantly if I have the book out with that java version, but works perfectly fine with the stock java version
tested it with only this mod+its dependencies installed, crashes every time I take the book out, instantly
debug.log

That log unfortunately shows nothing wrong, it just cuts off at the end where I assume the error happens. We'll need the actual error in order to tell anything, although I can't guarantee we'll really do anything about it due to you not using a standard jdk

I tried leaving it to do nothing for a long time, but that's all it does - just crashes as soon as I take the book out, and that's what the logs end up like - if I try it with vanillafix so it should display crashes, it instead hangs indefinitely until I force quit it with task manager - is there any other way I could force a log to occur?

Not that I know of, it's the jdk itself that's crashing. There's likely nothing you could do in minecraft that would change it

well, alright then - in that case I guess I'll try it again if an update comes out and see if it no longer crashes - would love to use this mod as it's so fun to make your own spells but the stock jdk just doesn't run well enough with the number of mods I have compared to this one
thanks for your help anyways!

Did a little bit more looking around and I managed to find a full output log and found the relevant crash info
https://pastebin.com/VQeHWWrY
looks like this is entirely an issue with OpenJ9, the java version I'm using. not sure why it's only affecting this mod, but looks like it's probably not anything on your side

OpenJ9 has very little support and has issues with several other mods. Change it.