The Configuration button is greyed-out and non-functional:

This is on

• Minecraft 1.16.4
• Forge 35.1.4
• AppleSkin 1.0.14

(Yes, I know the screenshot already has those, but I'm including them for indexing if this issue is searched later)

I'm going to close this and suggest using Configured for the NeoForge/Forge versions of AppleSkin. From my (limited) testing, AppleSkin integrates just fine with it.

Related follow-up for Fabric: #303

PR for config GUI in Forge is in the works MinecraftForge/MinecraftForge#8874

Forge removed the config GUI in 1.13, so it's currently not possible for mods to do anything with that button.

Ah, you're right

This issue depends on MinecraftForge/MinecraftForge#7395

1. For Forge, could this be re-opened with the forge and upstream labels?

2. For Fabric, it looks like the ModMenu API is actively maintained and provides a classic UX

(I took the below screenshots)

Looks like the Forge PR got rejected: MinecraftForge/MinecraftForge#7395 (comment)

I don't keep up with the Forge ecosystem so if a 'standard' library for this gains consensus in the future please add a link to it here.