the apt repo appears do be down:

W: Failed to fetch http://download.opensuse.org/repositories/home:/CZ-NIC:/knot-resolver-latest/Debian_12/InRelease  503  Service Unavailable [IP: 2a07:de40:b250:131:10:151:131:30 80]

Yes, opensuse.org had [outages] for a few hours, timed unfortunately around the release.  I think it's OK now.

[outages]: https://status.opensuse.org/incidents/284