+1 I have the same issues. "error: invalid target, create a target using the 'target create' command" in Xcode 13.x but not in Xcode <13. po not working when stopping on breakpoint in "random" source files. (100% reproducibly on affected files, but "random" as I can not see why / which files are affected and which are not)

Double check that the String in [OSSystemExtensionRequest activationRequestForExtension:@"HERE"... exactly fits the Bundle Identifier of your System Extension. If you are trying to build an Apple Sample (like "SampleEndpointApp") this is not the case by default as Xcode uses a variable in the Bundle ID ${SAMPLE_CODE_DISAMBIGUATOR}), while the one in code is hardcoded.