ok so i was playing with my personal modpack and when i updated to 1.2.1 the game started crashing.
i managed to narrow this down and it seems to be this mod

Crash log:
crash-2021-03-18_16.24.31-client.txt

using version 1.1.0 works just fine with no crash

tell me if i need anything else thanks

also this happens then you join a multiplayer server, unsure about singleplayer

java.lang.NoSuchMethodError: dev.tr7zw.transliterationlib.api.wrapper.entity.LivingEntity.isClimbing()Z You didn't update the TRansliteration lib.