Currently the only mod for Fabric that provides this is https://modrinth.com/mod/fabricskyboxes, and that one requires a converter to run. Maybe Puzzle could fill the gap and implement custom sky and clouds?

It may be better to simply add support for fabricskyboxes, users can add the mcpppp mod if necessary

https://modrinth.com/mod/fabricskyboxes-interop is now a thing