We bought our 2021 GLC300 6200 miles ago in May. It is a "base" version with virtually zero extras and only rear wheel drive. There is not an extra button on the dash to turn it on or off.
Adaptive suspension (or whatever M-B calls it) is not listed on the sales sheet, (nor is it shown in the VIN) but the car seems to have it, and the settings menu shows how to use it; as does the manual. (The menu offers E, C, S, S+, and individual driving modes.) (S+ mode turns that little I-4T into a ravening beast on the twisties: very satisfying. It has coil sprung suspension and has a lifetime mpg of 29 (so that's how I drive: like it was a Prius).

When the ignition button is pushed off and driver's door is opened, the car visibly drops one (1) inch. Every time. Witnesses have verified it does. WTF?