Some 30 years ago a family's friend owned a TR-182 Skylane (Turbo, retractable gear) and we sometimes flew around here in the Rhine-Main area around Frankfurt. Of course he used EDFE (Egelsbach) for take-off and landing. I remember asking him if it would be possible/legal to land in Frankfurt with his Cessna 182.
As I recall, he said they would likely reject such a landing as they wouldn't really appreciate us occupying a runway and make the big planes wait for our tiny one. Even if we were allowed, the landing and parking fees would be in such high regions that no one in their right mind would be willing to pay them.
The only exception, he said, would be an emergency. In that case we could very well land in Frankfurt but must be prepared for massive interrogation afterwards if the emergency wasn't obvious.
I'm not asking about a C182 specifically but about "small" GA planes (say MTOW below 2-3 t) on "big" German airports such as Frankfurt.