Apple's insistence to not use the common names never ceases to be annoying. "Private Relay" is oblivious DNS (https://datatracker.ietf.org/doc/rfc9230/) isn't it? That would be the reason internal zones aren't resolved. The relay and ultimate resolver wouldn't know how to resolve internal names.

Haven't seen Private Relay in action, does it also prevent mDNS? That would break a lot if it did.