All my games work the same as a non inmutable distro. Steam, Lutris, Heroic, Bottles, Retroarch, all those apps are on flathub, so ive never felt limited in that regard.

An annoyance i had with steam flatpak is when you configure multiple locations for installing games on the same drive. Steam will just show them all as "/var/cache/" no matter what youve actually set them to.

From what ive read, Steam flatpak is not an option for you. Bazzite is a variant of Silverblue but it has set up an arch container with the latest version of steam. They did this bc they considered it to use too many undesirable workarounds. Maybe that could work for you.