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The error looks correct. It very much appears you pointed to a directory instead of a package, so I wouldn't expect yum/dnf to know what to do. If you're trying to install a package, then you can specify it with http(s) if you want, but you'll have to have the URL point to the specific RPM. Alternately, maybe you were looking to add a new repository first and then yum/dnf install the package by a normal name? My guess is you're using some instructions that got chopped off and you were trying something more like

dnf config-manager --add-repo $REPO_URL

?

that message probably isn’t perfect on airgap. go grab the package you need from https://github.com/k3s-io/k3s-selinux/releases/tag/v1.3.stable.1

Yes, thanks @creamy-pencil-82913, I installed rpm from your link and problem solved.