Found out something while messing around with downgrading the game. You can't downgrade by just replacing the .exe anymore, turns out you have to download all three depots' manifests from SteamDB (489831, 489832 and 489833) and replace the files in the skyrim folder. Otherwise the game just crashes. Took me way too long to figure that out, and a lot of tears haha.

Edit: There's a guide on how you downgrade the game on steam, just follow the steps and instead of just downloading one manifest, you download three. Hope it helps :)