The game crashes instantly when loading, both on client and server. The ServerPlayerEntityMixin is probably being overwritten by another mod. The culprit is some setting from Carpet-Fixes, but I'll investigate further.

Full client log: https://mclo.gs/piWFHGL

Ok, without any settings in Carpet-Fixes being enabled the game still crashes. It's probably due to this Mixin: https://github.com/FxMorin/carpet-fixes/blob/1.20/src/main/java/carpetfixes/mixins/playerFixes/ServerPlayerEntity_spawnPlatformMixin.java

Yeah, the aforementioned mixin from Carpet-Fixes is clashing with the @Redirect in ServerPlayerEntityMixin, regardless whether the setting in Carpet-Fixes is enabled