Try to find out which mod adds the red square on your crafting grid and remove this mod
Its Quark. There is an option to show invalid squares, basically. Go into the mod's set up, click Client, go to page 2 and uncheck the show invalid slot (or something like that).
"We live on a placid island of ignorance in the midst of black seas of infinity, and it was not meant that we should voyage far."
There is no setting for that in my menu. I'm on 1.16.4 and I can't find it neither in the menu or in the config.
You can test removing quark from your mods-folder
Tried removing it now and it still occurs
Patchouli is twice in your mods-folder - remove one of it
and test it again
If it is not working, then it is caused by another mod
You can test it without:
I got it fixed, I removed some of the core mods such as valkyrielib which weren't being used.
Thanks for the help