

If you have the docker-compose.yml
locally, you can nix run github:aksiksi/compose2nix
to translate it into a nix file for inclusion in your nixos system config. I think that could be done in the config itself with a git url but I’m not that great at nix. You will surely still need some manual config to e.g. set environment variables for paths and secrets.
In the System settings, under Window Management > Window Behaviour, in the Focus tab, there is a Focus stealing prevention selector. If it’s set to extreme, then it does prevent switching to another desktop when I open a window that gets sent there.
I think that’s what you want but I guess it would mess with all applications, not just Steam. I don’t think you can do it per application.
I remember there being a window management protocol that would allow more control but I don’t think Kwin implements it yet.