It pains me to say it, but the most viable solution for "normies" going Linux is to use one of those new inmutable distros. The major corporate distros seem to be going that way and others will follow suit.
I understand your point, but I don’t see immutable distros becoming the primary solution for most Linux users anytime soon. Immutable systems offer strong stability and security by limiting changes to the base system, which can definitely be helpful for new users or corporate environments, but one of Linux’s biggest appeals is its flexibility and customization. For a lot of users the ability to freely tweak and control their setup is what draws them in.
While some major corporate-backed distros are embracing immutable models, it’s likely that traditional, mutable systems will continue to dominate for users who want control and flexibility. The Linux ecosystem is diverse, so immutable distros will probably remain as one option among many rather than the standard.
Anyway, the immutable distro that most closely resembles SteamOS is Bazzite:
https://bazzite.gg/