@praiskup Could you please check this one?

This has been added to the CPT's TODO list (3-months schedule)

I believe the issue is a little bit different.
Both dnf5 and old dnf4 setup the copr repository in the host (when used with --installroot) but on subsequent runs with --installroot dnf5 doesn't see it by default.

This is because dnf5 no longer tries to automatically search for configuration file and reposdir in the host if it doesn't find them in the installroot.
There is now --use-host-config, see https://dnf5.readthedocs.io/en/latest/misc/installroot.7.html#installroot-parameter.

Recently we have added a helpful message when no repositories are found in the installroot which I think would help in this case.

So using empty installroot /tmp/test/:

$ dnf5 copr enable rpmsoftwaremanagement/dnf-nightly --installroot=/tmp/test -y
...
$ dnf5 update dnf5 --installroot=/tmp/test
Updating and loading repositories:
Repositories loaded.
Failed to resolve the transaction:
No match for argument: dnf5
No repositories were loaded from the installroot. To use the configuration and repositories of the host system, pass --use-host-config.

(new --use-host-config hint)

Unless we want to change how the copr enable command behaves I think we can close this.

Unless we want to change how the copr enable command behaves I think we can close this.

I think this is exactly the thing we want to do - dnf copr should manipulate with repofiles in chroot, not on host. That said, not just enable but list, delete, etc. For DNF5 at least (I thought DNF4 is fine per original report, but haven't tried myself).

I am working on this one