Pretty much any car that comes with even a very basic cruise control will have a speed limiter option. My car is from 2010 and has it. I think my 2004 Mégane I had beforehand may have had it too, IIRC.

Although it’s a bit more fiddly than what you describe in that you have to turn off cruise control mode, switch to speed limiter, set the speed, then activate.

But yes, it would be an interesting feature to have a “town mode” button that you could set to 20 or 30mph in the car settings. Much more streamlined than the above. I imagine you could do other things, too like trying to keep revs to a minimum to keep the car quiet, (if a hybrid) going EV-preferred or EV-only, etc.