It sounds like this - running a full desktop Linux VM - within Qubes is not really a common use case, and not really “supported”. (As opposed to running a Windows, which is common and “supported”/documented.) Is that correct?
In this case, if literally nobody here can report success with this use case on Qubes 4.1, I’d rather just give up instead of trying to swim against the tide.
I might sadly be better off finding an online file/text sharing tool for my copy/paste and file copy purposes.
Is it somehow possible to go the other way around? Start with a normal Qubes AppVM and somehow “enhance” it into a full desktop experience (without having to bother with HVM/Standalone)?