Ingo,
I just posted this: Guide to Direct Drive Trainer Cassette Spacing
My advice is to start with the instructions in the linked thread above - measure cassette to dropout spacing and determine if they’re different.
If the problem you’re having is the cassette is sitting too close to the drive-side dropout, AND at the same time you have no more spacers to remove, the solution is you need to add some type of spacer to the drive-side to increase cassette to drop-out distance.
While a bent derailleur hanger would lead to issues, we can eliminate that as a possibility if the bike is shifting fine while the wheel is installed.