This is the factory BMW oil filter cap wrench. 86mm, 16 flats.
https://www.fcpeuro.com/products/bmw...40-83300493936
There may be cheaper alternatives, but I have found you rarely regret using the factory approved tool. It will fit without damaging the plastic cover, and simply works. Unless another tool has been vetted by other users... I've been down that rabbit hole trying two or three until one works without slipping off the cap or filter. I've had some work for a few uses, then go to sh*t. Of course right when I am trying to get the proper torque setting....and its slipping off.