I managed to get round this by copying Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/DeviceSupport/13.4 from the latest Xcode.xib into my installed Xcode package.

I can now debug 13.4 devices on Xcode 11.3.

My stress level has gone down dramatically since I gave up iOS development and went back to the web. I think it’s a better career move long term too.

What??? Xcode 11.4 requires Catalina now?? That’s nuts.

Over the last few years Xcode has dropped support for older versions of macOS very aggressively. It requires upgrading to a new major version within the year that the new version came out, and quite often requires the latest minor version as well.