Status code 500 indicates an error at the server end. It’s relatively
common with Fedora mirrors for some reason.
If you are using the apt-cacher-ng package that I provide I try to keep
the package updated with extended fedora repository lists and
configuration changes. It works well for 40 and (most of the time) 39.
I never presume to speak for the Qubes team.
When I comment in the Forum I speak for myself.