Universal Tweaks - UniversalTweaks-1.12.2-1.9.0.jar
Mixinbooter - !mixinbooter-8.8.jar
Forge - 14.23.5.2860
mc 1.12.2

So universal tweaks is telling me I need mixinbooter 8.0 or above and that my installation of mixinbooter8.8 is apparently missing.

no idea why this is happening

latest.log

debug.log

Try launching without FermiumBooter. It does the same thing as MixinBooter, so it will probably cause unintended behavior. This means you probably need to use CensoredASM for now instead of FermiumASM. If it still doesn't work, try disabling the Essentials mod as that also has issues with MixinBooter.

Can confirm it's this. Many things were changed within Fermium. Making it incompatible with the following so far.

Vintage Fix
Modern Splash
Universal Tweaks
Config Anytime

It's a question of support being added I'd assume.

As of now, Universal Tweaks is solely built around the infrastructure of MixinBooter, using its designated mixin config functionality as well as features from MixinExtras. Can't provide support for other mixin loaders from within Universal Tweaks.