I’m fairly certain you could still run that shell script on steamOS? I don’t understand why an immutable distro would keep you from doing that. It’s essentially what Lutris and Heroic Games launcher do.

You can even install KDE connect on windows though, I imagine its pretty DE agnostic.

If you don’t want to code it, give Publii a look. Otherwise, my go-to is Eleventy, simple and clean.