Linux distros designed to run "Live" (formerly off a a CD, but nowadays a USB or) are approximately immutable. A couple good examples are Tails OS and the vener

Linux distros designed to run "Live" (formerly off a a CD, but nowadays a USB or) are approximately immutable. A couple good examples are Tails OS and the venerable TinyCore Linux distribution. I also agree with many other commenters about inclusion of NixOS and GuixSD.