Over on this thread, someone recommends creating a new (macos) admin user and using that. I wonder: Could this be related to using a non-admin user (as best security practices suggest)?

Same here, I do not want do spend € 99 on writing a simple learning app for my six year old.

Follow-up: Apparently this has been fixed for single level subdomains like foo.apple.com but is still not correctly implemented for multiple levels like foo.bar.apple.com iOS 15.4.1, iPhone SE 1

I filed a bug report at https://bugs.swift.org/browse/SR-16062