I have very little familiarity with most immutable distros and I don't know how difficult they are to make necessary configurations to system files. If I can't change things that need to be changed, that's an issue for me.
That said, I've just started looking at NixOS, which is immutable from my understanding. It looks incredible, because you preconfigure everything exactly how you like in a config file then build the system from that config. It seems like the best of all worlds - total control over your system to configure it how you want, multiple easy fallbacks if you mess something up, no worries about forgetting what changes you've made or how to replicate/undo them, and the security and unbreakability of an immutable filesystem. For the first time since I started daily driving Linux, I think I'm going to distro hop.