You can go with something like this if you want a clean solution.

I use a drive dock station for my backup drives, and I have a few of these for one-offs too.

I’ve been very happy with both Silverblue and Kinoite. I’ve installed it to all of my workstations now and can’t imagine ever going back to a traditional distro.

Your comments suggest that you’re already aware of distros like Silverblue so, if I may ask, how are these different than what you’re looking for? Silverblue comes with several flatpaks installed, but you can easily remove these and you’ll be left with a pretty barebones ostree image.