Not immutable, but I slapped Garuda on a 2016 gaming laptop to give it a second life and it’s been great for the most part. I got a bit fiddly with it and had to fight my way through some partial upgrade issues, but know I arch based distros better and it’s stable as can be. I honestly don’t update it that often since it just serves are my TV box, and I’m seriously considering swapping to a Nix install now that I’ve mostly stabilized my package list for the purposes of gaming and video encoding. Proton is one of the only things I think get regular updates on that device, but those are entirely handled by Steam, so immutable is very attractive to me for a gaming only system.

I’ll also add that my primary device has arch on it and I do most of my gaming (but also work) there. It’s great, and I can’t help but feel a lot of the distros that are “made for gaming” suffer from a lot of the issues that windows does. They are trying to be preconfigured to work with any and all hardware. This leads to bloated package lists, and just extra guffins to work around as you trouble shoot. I’d say my arch install took a bit longer to get gaming super stable, but I’ve also had to fix much fewer issues compared to the Garuda install.

All the people mentioning Bazzite are making me eye it to replace Garuda tho.