Cooper S doesn’t start, just gives a “crack” sound (battery is ok)

Hi, I have a Mini Cooper S R53, yesterday I drove 200 kilometers without any problems. This morning I wanted to work quite normally, But there was only a crack noise. Engine does not start, or turns.. Battery came new 2 years ago. I then called the Adac. The checked the battery, and it is perfectly fine. He then tried to bridge the front of the engine compartment and then directly at the back of the battery. Both without success. More than the clacking did not come. Then me And then he tried to push the hand. Of course he didn’t. Then he said something was blocking the engine. Can that be? I mean, if a gear is in place you can’t push it at all, right? Does any of you have any idea what it might be about? Thank you in advance!!