Switched to an immutable system after I finally managed to wrap my head around the concept.
I've tried it before but left frustrated cause my normal workflow doesn't apply anymore.
But if you're looking for an OS that basically disappears in the background, it's great. I even removed the terminal cause I have no use for it on my laptop.
Generally I use my computer to launch programs that do the stuff I want to do, or edit my files.
My files are in /home and programs for the tasks I need are available as flatpaks.
So I don't need to rummage around in the rest of the file system. You could call it "a laptop for grandma" except I'm not that old. I use my laptop for office stuff, gaming, photo editing, streaming music and video, browsing, mail, messaging, ssh'ing into my servers, etc. What I don't use it for anymore is tinkering with my OS. I'm fine with default Gnome and I don't need to adjust every little thing, I can just adjust myself a bit to how the GUI works.
I just don't want to read Arch news before I update weekly, set apt-pinning priorities to disable snap, deal with recommended dependencies, meta packages, mirrorlists, third-party repo urls, gpg keyfiles, file permissions, executable flags, systemd services, and all that jazz anymore.
Yeh, immutable distros... You can install software, it's just you have to declaratively define what software you want, then apply that as a patch.
You don't just apt install cowsay, you have to create a file that defines the installation of cowsay.
This way, if you have to change how cowsay is installed, you tweak that patch file and reapply it.
If you have to wipe & reinstall (or get a new computer or whatever) you just apply all your patches, and the system is the same again.
You're talking about declarative systems like Nix. Immutable just means that the root filesystem is read-only. You can install programs as Flatpaks or inside a container (toolbox on Silverblue).