Google started testing the dark theme in the Google Maps application last year, but only now added it to the stable version of the program 10.51.1.
A user on the Reddit forum wrote about this. The innovation is distributed server-side and so far only on Google Pixel smartphones with Android 11 on board. In the near future, Dark Mode in Google Maps should also be added to other smartphones.
As shown in the screenshots, you can enable the dark theme by default or choose to change automatically, depending on the system interface. By the way, if you, suddenly, did not know, then all users of the Google Maps application now partially have Dark Mode. It turns on in the evening in navigation mode.