As per title, I get the experimental settings warning even on a clean world in a clean instance with nothing else installed aside from Quark and AutoRegLib. No other mods, no resourcepacks, no shaders, no datapacks.
Minecraft version: 1.18.2
Forge version: 40.1.16

Logfile: latest.log

PolyMC log output: here.

Screenshots:

This is just kind of a base minecraft thing now. If you want to disable that warning, several mods (including Terrablender) disable it.