Apologies, I thought I had tested, but I copied without the 'module' command, it should be:

$ sudo dnf --enablerepo=updates-testing-modular module install ghc:9.0/default

Alternatively you can run, eg:

$ sudo dnf --enablerepo=updates-testing-modular module enable ghc:9.0

$ sudo dnf --enablerepo=updates-testing-modular install ghc

etc

It should go stable in about a week.

Thanks, Jens