Okay, here is the TL;DR as a solution for Fedora Workstation users as said before:
Add the correct metalink and remove baseurl.
I.e.:
[fedora-cisco-openh264]
# ...
metalink=https://mirrors.fedoraproject.org/metalink?repo=fedora-cisco-openh264-$releasever&arch=$basearch
#baseurl=https://codecs.fedoraproject.org/openh264/$releasever/$basearch/
# …
[fedora-cisco-openh264-debuginfo]
# …
metalink=https://mirrors.fedoraproject.org/metalink?repo=fedora-cisco-openh264-debug-$releasever&arch=$basearch
#baseurl=https://codecs.fedoraproject.org/openh264/$releasever/$basearch/debug/
# …
As said before by @rjl931189261, Silverblue users can just copy/correct the correct file: