ahh, then we were talking about different things, ;-D my mistake.
So about my problem:
If I lock the screen, then I have to leave after the first lock 1 finger on the screen and with the 2nd I can then operate. This also remains in the activated system.
If the screen is then locked again, 2 fingers must remain on the screen and I can operate the smartphone with my 3rd.
It feels like after each screen lock a counter goes up in the background that lets me use one more finger.
If I turn the smartphone off and on again, I can operate it with one finger until the first lock.
Edit: with a USB mouse everything works, probably because of the touchscreen