I know that some manufacturers ship QubesOS, those are intended for people with high threat models afaik.

I find ZFS rollbacks to be easier but setting up ZFS can be a pain (other than in Gentoo and NixOS from my experience), so take your pick

As someone who’ve tried Gentoo on systemd and OpenRC, as well as Void with runit, I don’t see any reason to use OpenRC over systemd. I never noticed any performance difference, and it has far less features. As for runit, if half the boot time for half the features is what you need, then go for it.

I use ZFS, not BTRFS, but both have snapshots, and if you’re someone who likes to tinker with their system like me, it lets you do so without worrying that it will break.