Thank for this excellent write up. I just completed the install on my 2021 M340I XDrive. My advice based on what I read and doing it is this: Start at the lowest point when separating the plastic housing. Closest to the dash. It was the only place I could get a tool started. I broke no pieces doing it this way. I will include a few pictures and links to both the mirrortap and the inexpensive mount I bought
Mirror Mount
https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1
Mirrortap
https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1
PS. Wiring as shown in this post results in my detector shutting off in approx 5 minutes. Thank you all for the incredibly helpful post