I noticed that you are interested in immutable distros! That’s a good choice for your requirements, since it allows you to skip troubleshooting most issues by rebooting or performing a rollback.

I myself am happily using NixOS, but I think its advantages only shine when you want to spend time configuring your system. That being said, if you want to invest that time once and you stay on the stable version, you can also have quite a stable experience.

The other two options you listed are both atomic Fedora spins made by uBlue, which add minor customizations to the base image. Both of their non-GNOME seem to be based on Fedora Kinoite, which would be another option. Fedora is generally more opinionated, which is good if you don’t want to tweak anything.

Between these Fedora images, I’d recommend Fedora Kinoite for simple setups and Bazzite if your focus is on gaming. I have never heard of Aurora before and it doesn’t seem to add that much. That being said, if you want to try out multiple of these options, you can always rebase your current atomic Fedora desktop to another image!

You can use glim or build your own tool using grub. Edit: The article on Arch Wiki describes the manual process and also list more automated alternatives.