Have you checked out OpenSUSE MicroOS at all? It’s similar to Silverblue. Runs great on my Framework 13 with Intel 13th Gen.
I wouldn’t be too concerned with “officially” supported Linux on the Framework. It is a very Linux friendly machine. The folks they have supporting Linux are active in the Framework forums and very helpful.
I eventually went back to my tried and true Debain. I loved the immutable OS thing for all the reasons people have listed here. My one issue was direct access to external devices can be a pain. IE: I just could not get USB passthrough working with virt-viewer after all my fiddiling.
Debian Testing + flatpak
Testing is shockingly stable, kind of up to date, and rolling. Since you will use Flatpak for all your apps it really removes a lot of risk that dependencies will break an app.
I use this combo as my daily driver for my work PC, knock on wood it’s been super solid!