Kind of a funny "shower thought" to think about. Well if it were an iOS or Android device, the "jailbreak" is rooting since root is highest level access for *nix systems. So that is what is technically happening with the Steam Deck as you now have sudo access and most/all read-only restrictions are off. But at the same time Valve doesn't start banning your deck or punishing you for doing it, and even tell you how to do it in an FAQ on the official Steam Support page. Which means it isn't technically a "jailbreak" either and more of a "advanced settings" with some warnings and specific instructions that aren't defaultly turned on. So it is both technically "jailbreaking" and not "jailbreaking."

I would say no as it was designed to be turned off if desired to do so. If it weren't designed for that, then I would say yes.