I am having a similar problem with Xcode 12.2. My extension seem to work elsewhere, but not in Text views.

I have this same problem in a macOS project. It seems if there are multiple items with .automatic placement, all but one are hidden. This seems to be either a bug or undocumented behavior. The documentation is highly unreliable. Some placement options like .navigationBarLeading and .navigationBarTrailing are stated to be available in macOS 11.0+ but the compiler produces an error ("'navigationBarLeading' is unavailable in macOS") when used. And using .principal placement usually has a runtime error and crashes. Any help out there?