I’m not local, but a friend of mine sometimes takes part at the “Standert” Bicycle Thursday Rides: https://standert.de/pages/feierabendrunde-2020 (Not atm because of covid restrictions, but hopefully in spring again). Probably a good spot to link up with like-minded folks. They also have a few routes on their page: Ride Solo | Standert Bicycles | Berlin
Have fun and welcome to Germany!
Chris