As a (new) NixOS user too, I'd be interested to hear more about this.

Have you tried setups like "Erase Your Darlings" and "NixOS: tmpfs as root" to explicitly persist and manage state?

https://grahamc.com/blog/erase-your-darlings

https://elis.nu/blog/2020/05/nixos-tmpfs-as-root/

Nope, but that's exactly what i had in mind when i said "put everything in my nix config". Any setting for my desktop, browser, etc would need to be in that config. The tempfs would just help me practice it.

Big PITA though, imo. At least until i'm "better" at Nix.

I spent about 3-4 months learning Nix/OS this past spring/summer. After some trial and error and source code spelunking, I finally got my system working according to these two blog posts, with some tweaks [1]. It was a lot of work to ramp up that learning curve, but now that I have I don’t think I can ever go back to another standard Linux again. They all feel so messy and disorganized now by comparison.

[1]: Some things, notably containers like LXC/LXD, can’t work with tmpfs mounted to /var, /var has to be on disk, while the rest of / can be tmpfs.

For a non-Nix user, what do you mean by "app state"? Things like config files?

Correct. Though sometimes apps also store little files as local databases, effectively, and switching versions of the apps can jack with that file as well. Making rollbacks more difficult

Could you elaborate a bit on this? Not arguing, genuinely interested ...

I'm surprised the app state isn't backed up so that rolling back restores it?

you can use fs snapshots and backups