SteamOS is optimised for Valve’s hardware, and at present it only officially supports AMD GPUs, and not all of them. They are rolling out support for more AMD hardware, and “working with” Intel and Nvidia to do the same. Support is a big deal, especially as it’s an immutable system and it’s not got a big ecosystem of users/volunteers managing the packages and providing alternatives. Configuring and modifying it is more difficult than a non immutable system, so you are very dependent on the official options the distro provides to customise your system. It’s based off Arch which is completely different to Bazzite. Arch doesn’t have it’s own immutable versions to work with (there are immutable distros based on Arch, but not ones that SteamOS is based on), so if you need to problem solve you’re restricted to SteamOS specific advice, and whatever Valve currently has within it’s repos. It’s likely 3rd parties will add more options but at present it’s a focused distro.

Bazzite meanwhile is an open distro project, which is also immutable but built from the start to support (and tested on) a huge range of gaming PCs and other hardware, including with Nvidia GPUs. There are lots of users & volunteers already involved that are motivated to ensure it works with all the major graphics cards, and keep up to date as they use it themselves. It is also based off Fedora Kinoite, which has an established immutable ecosystem which eases some of the friction when finding support. This also means likely more software within the main Bazzite repos already tailored for the immutable system, alongside the usual options in Flatpaks and AppImages. But Bazzite also includes Waydroid to allow android software use, and is already set up with Homebrew & Distrobox to give more options. It’s unlikely SteamOS has these things set up or at least easily set up for users.

With an immutable system it’s important to have options to get software installed, although it’s possible in a HTPC set up you’ll find what you need in the main repos of SteamOS, Flatpaks and AppImages so maybe it won’t be an issue.

SteamOS is a great concept and I like it on my Steam Deck, but it’s not really something to run on your devices while so early in it’s support system. If your device is AMD based then maybe you’ll have no issues, but I don’t think being an early adopter on a system you want to use daily is a great idea. Maybe you won’t need the wide range of software and options Bazzite offers, but Bazzite does offer much more “out of the box” at the moment as a mature and established distro.