Mods: Unique+Enchantments+Base-1.16.5-1.4.3.1, ModernUI-1.16.5-2.7.1.105

@wasdspace moderUI doesn't support custom fonts which is a Vanilla Minecraft feature.
Not a UE bug but a Modern UI Bug.

To correct Speiger here:
Modern UI overwrites the Font used, the Icons are done with Fonts.
This is an inherent incompat, you need to change the font used itself and not overwrite it

To Correct Xaikii:
He doesn't test if the Font being set was already overriden, AKA he blindly just overrides all fonts being set.
All he has to do is: "Is this a custom font? Yes? Then don't override it. No? Then override it"