When updating a mod using Cloth Config from Minecraft 1.20.6 to 1.21 annotated with a custom background (like @Config.Gui.Background("minecraft:textures/block/white_wool.png")), the actual background becomes black:

(This actually appears to be layers of translucent black repeatedly rendering over the old screen, but this effectively becomes black after a brief moment.)

Using:

• cloth-config 15.0.127
• fabric-api 0.100.6+1.21
• modmenu 11.0.1