Not a problem with Framework hardware. Framework publishes all UEFI/BIOS and other firmware updates on LVFS so if your distribution supports fwupd you are good to go. The only catch is that most of the distros disable automatic firmware updates by default, so you will probably need GNOME Firmware or become familiar with fwupdmgr.
The only one troubled devices now is original Laptop 13 (11th gen Intel) which is stuck in beta channel on LVFS due to some kind of issues with Intel ME. Here is a link to a mostly true post in the LVFS thread.
I am not sure what do you mean. Like SteamOS proper? AFAIK nobody does that since Valve never released a public version. Everybody who wants the most SteamOS-like experience use Bazzite with Steam Gaming Mode enabled.
Among millions of QoL stuff, Bazzite always has the latest kernel version opposed to whatever version Valve ships in SteamOS (I assumed it is some kind of LTS, but Gemini says otherwise, anyway it is definitely not the latest one).
Bazzite is also officially supported by Framework.