For future reference you were using an old guide from 4.2 that had been
tested on an old Fedora. My guess is that the iptables rules in that
script worked poorly if at all on Fedora 43 in r4.3
As you are now running with Mullvad (good choice) I have little
inclination to troubleshoot further.
I never presume to speak for the Qubes team.
When I comment in the Forum I speak for myself.