1. The reason you're getting "Error: Unknown repo" is that the
repository name is not "qubes-repo-contrib". Rather, the name depends on
your Qubes release and whether it is in dom0 or a TemplateVM. For
example, in a Fedora VM on Qubes 4.0, the new repository is:
/etc/yum.repos.d/qubes-contrib-vm-r4.0.repo
2. After I installed the repository in a Fedora VM, I checked and found
that it was already enabled, so --enablerepo is unnecessary.
3. I then tried to install the "qubes-tunnel" package in the same VM.
Even though dnf reported that the contrib repo was checked, the
"qubes-tunnel" package was not found. So, I can at least partially
reproduce this. However, I don't know whether this problem is specific
to the "qubes-tunnel" package.
I suggest filing a bug report.
--
Andrew David Wong (Axon)
Community Manager, Qubes OS
https://www.qubes-os.org