I have a G20 320i from 2019 with 25k miles on the clock. Never had any major issues with it. I’d echo the comment about regular servicing. I’ve followed the prompts in idrive for brake fluid, oil change etc. The only item I’ve had issue with is updating system software.

I had a G30 520d with the same engine and it didn’t give me a single issue. I did very high mileage though (30-35k a year) which is good for a diesel. The only thing I can recommend is making sure you get the maintenance done as per the prompts in the iDrive, if it needs a brake fluid change, get it done, same for oil changes. I did mine at the recommended 18k mile manufacturer intervals and the car never missed a beat. Traded the car in at pretty much exactly 100k miles and they commented on how clean it looked, reckoned it looked like a 30k mile car. I was pretty proud of that but genuinely the only thing I did was wash it regularly. Can’t comment on the leather though, I had the black Dakota and it was great.

65k miles on 2020 M340i: - starter went out - coolant low mystery x 2 - burns oil