I was able to get xcframework + simulator fat binary working. I needed to have an xcframework that supported simulator on both arm64 and x86_64 because I'm developing on an M1 and my CI provider wants x86_64 to run unit tests. (Oh, and having an xcframework that can be used to develop on Intel might come in handy at some point.) My steps: Build three frameworks (in my case, arm64, arm64-simulator, x86_64-simulator) Build xcframework with arm64 and arm64-simulator frameworks Use lipo to add x86_64-simulator binary to the arm64-simulator binary (which is inside my xcframework) That's it. I ended up modifying my xcframework's Info.plist file to document the fact that the second "library" was a fat binary (adding "x86_64" to the "SupportedArchitectures" array) but that doesn't appear to be necessary.

What an incredible bug! On Xcode 14.3.1 and, yes, encountering this error where I build, get to see my compile errors for a second or two, then have them helpfully disappear. Clearing Derived Data did not fix the issue for me.