I am using 1.16.3 MC, 34.1.42 Forge, as well as a couple mods(I don't believe this is a mod issue, no mod things in crash log.) No Optifine at all. When mod options is selected in the title screen, and anything is clicked in the mod options, the game saves the world and crashes.
Crash log:
https://pastebin.com/27DHC140