You may be happy, or perhaps dismayed, to learn that I finally installed Bazzite on my desktop.

Well played! Welcome to the cool kids club! I've actually used Bazzite myself for a short while a couple of months ago. It felt like a holiday destination with lots of cool stuff, but it was more opinionated than what I'm comfortable with. So I returned back home (read: custom uBlue image) afterwards, where I am in command for what's found inside and where I am free to do whatever I will. Though, I did pick up some of the things I liked from Bazzite 😜, so it was not for naught 😉.

I did a bit tonne of sampling, with BlendOS and Vanilla, trying things out, but Fedora wins.

Very interesting! I've got my own reasons for preferring Fedora *cough* security *cough*, but I'm very interested to know your findings! I'd have to admit that Vanilla OS' upcoming 2.0 Orchid update is very tempting though.

I have Fedora Silverblue on a usb in case Bazzite does not like my computer,

Hmm..., perhaps consider the following:

1. Rebase back to Silverblue with rpm-ostree rebase fedora:fedora/39/x86_64/silverblue (assuming you're already on Fedora 39).
2. After you've booted into Silverblue, pin the Silverblue-deployment with sudo ostree admin pin 0.
3. While still in the Silverblue-deployment, rollback to Bazzite with rpm-ostree rollback.
4. Reboot, and you should notice that you have one additional entry in the GRUB-menu. That's the Silverblue-deployment where you can always fall back on; just in case*.

The above steps do assume that you haven't pinned any prior Silverblue-deployments; as you don't necessarily need multiple Silverblue-deployments 😅. Furthermore, they assume no additional steps involving Nvidia; but that's mostly because I don't have any experience dealing with that (thankfully).

I swear I will just jump onto the NIXOS (or guix) bandwagon if I ever decide to switch again.

FWIW, you can install both Nix and Guix on Silverblue.