Now I have started to try it and thanks many tips from the great community and trial and error I am a bit cleverer.
Even if probably most people know it, but the parameters 20 and 21 do not necessarily have to be programmed per raw configuration. The parameters 20 and 21 are the first two entries in the advanced settings:
For whatever reason, Athom has forgotten the explanation for the parameters and the translation into other languages is also missing.
You can connect a reed contact to input 1 (IN1 + GND) and/or input 2 (IN2 + GND).
The parameters 20 (IN1) and/or 21 (IN2) must then be configured to NC (Normale Closed) or NO (Normally Open). It depends on the reed contact and how you want to use it.
For example, if you have connected the reed contact to IN1 and configured it to NC and remove the magnet (similar to door/window sensors) then an alarm will be reported on input 1.
Open ---------------------------------------------> Close