On E20 fuel, you don’t have to worry at all. In fact, you should be happy because the base octane rating for E20 fuel has jumped from 91 octane to a minimum of 95 octane or even higher. Hence, this suits the 11.0:1 compression ratio of the M340i’s B58 engine, and now, instead of hunting for high-octane fuel, you can use fuel anywhere, as you are now assured of 95 octane. A bigger concern are the low profile tyres, which are staggered with 225/40 R19 in front and an even lower 255/35 R19 at the back. This could be a problem on bad roads, where the tyres could be vulnerable to impact damage.
One way to protect the tyres against punctures, but not guaranteed, is to pump up the tyre pressure by about 3-4PSI to make the sidewalls stiffer. This reduces the flex in the sidewalls and makes them more resistant to impact damage, but quite honestly, the BMW M340i is not a car we would take into the jungle! 
