IMHO you should first figure out what exactly happens/goes wrong with your Ubuntu installations.
Immutable distros might or might not be a solution, but if the core of the problem is really the quality of the Ubuntu updates for example, you could try to run Debian (stable).
But again, the suggestion to use Debian is throwing a solution in the room which might not fit your problem.
Just as a reference point: I am running Debian stable on Laptops, Netbooks, Raspberry Pis and in virtual machines (AMD64/AArch64) and have no weird bugs, everything works for years now and runs smooth.
Concerning the Steamdeck… I love them, they run perfectly fine, but unless you are tweaking them/do more than run games, you cannot really compare them to what happens on your desktop.