No reason to use SteamOS, it's just immutable Arch with an A/B partition scheme. Modern SteamOS is designed specifically for the Steam Deck and they only ship it as a recovery image for the Deck.
You can install Steam on whatever distribution you want, I use the Flatpak, and just enable Proton in the compatibility settings.
And if someone’s after that console-like functionality, ChimeraOS is the right choice in this area. It behaves like SteamOS, but is more compatible with PC hardware.
I'm pretty excited for the Cosmic DE later this year. Here is a demo given by the CEO and the design lead. The audio isn't the best, but good enough. This is probably the most excited I've been to try out a new operating system since OS X Tiger. It is being developed by the Pop OS team, but they are making it so anyone can use it, Fedora plans on having a spin, I believe it's out there for Arch, and I'm sure others will have it as an option. Though I wouldn't use it as a daily driver until it's actually released.
You can install Steam on whatever distribution you want, I use the Flatpak, and just enable Proton in the compatibility settings.