I own a 2020 M3 and a 2021 MY. For some reason (the M3 is fine, but) I find the lumbar support in the MY way too excessive, even when completely deflated. The seat is extremely uncomfortable and causes pain in my lower left back. I had the exact same issue with in 2 other cars I owned (Honda, Mini) - so I know it is my personal problem... The Mini originally had a fixed lumbar support and what solved the problem was installing a lever-operated lumbar and taking it all the way off. So - I had to find a way to further flatten the MY's seat...
Solution: I removed the seat cover (many posts detail the steps) and then removed the 10mm bolt on the bottom of the yellow seat support. I then placed the yellow part on top of the metal bracket to allow it to move back and closed the seat cover. Now the seat has MUCH more "give" in the lumbar area. I drove the car a couple of times for short distances and the initial results are very encouraging.
Solution: I removed the seat cover (many posts detail the steps) and then removed the 10mm bolt on the bottom of the yellow seat support. I then placed the yellow part on top of the metal bracket to allow it to move back and closed the seat cover. Now the seat has MUCH more "give" in the lumbar area. I drove the car a couple of times for short distances and the initial results are very encouraging.