Crash Report

Minecraft 1.17.1
REI 6.0.266-alpha
AppleSkin 2.1.1

Looks like renderTooltipInner got split into Fabric/Forge versions. Here's where the new Fabric version lives:

https://github.com/shedaniel/RoughlyEnoughItems/blob/6021d6e84f4609a98b823c507848d44e8eba078b/fabric/src/main/java/me/shedaniel/rei/impl/client/gui/fabric/ScreenOverlayImplImpl.java#L41

The fix might be as simple as updating the target class and the method signature in AppleSkin's mixin.

Glad to know it's a simple fix

Thanks for reporting the issue. Should be fixed in v2.1.2.