I had the same problem and dealer told me it could not be changed BUT I researched in the owners manual for a long time and finally did find a way to disable it, sorry but I don't remember what it was or exactly where I fund itBe careful for what you wish.... I have this option which I find very annoying. It forces my GLC to slow to the speed limit.
So, if I set my travel speed to 45 mph, and the limit is 40 mph, it will override my preference.
This is particularly annoying in school-zones (USA) where the speed limit is 20 mph.
First, there is no school on weekends, yet the MB still slows to 20 mph.
Second, children during COVID are staying at home anyway. No need to reduce speed.