Yes but again, Flathub Firefox has no process isolation with user namespaces. Something not easy to understand, but it simply removes a big security layer (between browser and processes, and between processes). It also adds the security layer between browser and OS, so not that easy.
Have a look at bubblejail, that is far away from plug and play poorly. But it allows to sandbox the browser like flatpak, but allow user namespace creation (a syscall) to also isolate processes.
Ublue is Fedora Atomic without legal restrictions or strange decisions.
But they also deleted their old website, so the only easily installable versions are Bluefin/Aurora (GNOME/KDE) and Bazzite. Which are also opinionated but I think in a good way.