So first of all, you could likely still access your drives when you boot from a USB. Goes for any OS

secondly: if you play with fire, don't complain about the blisters. And yo be clear, with fire I don't mean Linux, with fire I mean specialty distro

You need to ask yourself what you want. If you want something shiny and cool that does certain security things that are awesome but not really that needed for the average Joe, then fine, go with whatever.

I on the other hand need a Linux distro that works, that I can trust. I have been using Kubuntu (Ubuntu with KDE UI) for over the last 20. There are bugs, like everywhere, but bugs like "this little widget doesn't respond right", not "oh my OS suicided again"

Going from CachyOS to NixOS because you bricked something is wild. You very clearly have no clue what you're doing and I regret to inform you that your choice of distro will not make an impact. But it isn't all bad — you could stop panicking and acting like you know what you're doing and learn about the technology you're trying to use.

Or keep switching distros forever. I'm sure that will work too.

What would your ultimate distro be like?

The one that fits one's needs the best. Given your frustration with unstable systems, I'd say the best ones would be those that take longer to make major updates, like Debian, Mint and Slackware, as then issues aren't introduced as frequently, and older ones are better known and easier to fix or even preemptively circumvent.

I've really enjoyed NixOS the past few years. I think if I started over with it I'd be less ambitious about making it an impermanent setup over ZFS. It's not a particularly enjoyable experience to set up as bugs abound with ZFS specifically. But other than that initial highly experimental choice at the time its been stable. I hope you enjoy it as much as I have!

I'd make the same point as everyone else - choose a distro that suits your needs better - but it seems already made several times.

I've used Linux both personally and professionally for a long time but I just don't want to tinker/break my main desktop. I am currently using bazzite, and while it's not perfect I've found it great in the not breaking department. The immutable part takes some getting used to though. The recent drama around it is annoying though.

I'd be cautious with nix, while it's reproducible you might end up having to put a lot of effort into making it what you want. If you want that experience then by all means, but it may just frustrate you further if you do it on your main machine.

Fedora w/ KDE always just feels like home to me, I like the defaults so I don't spend much time mucking around, and it feels stable and reliable.