1. The Pax dense is very low, but GSX for example shows boarding of 160 people and it takes more the 20 min. I will reduce it in about 10 minutes.
Have you READ my previous reply, which included a quote from the manual, clearly explaining why this is exactly what should happen, if you keep your density low ? I think you misunderstood what Passenger Density means. It doesn't mean "Less Passengers", the number of passengers is always the same. It means "Number of passengers seen at the same time on screen" so, clearly, the low you set it, the MORE it will take to board the SAME number of passengers, which never changes.
2. I was on a position in EDDM where Sode was not available and now my passenger walks trough the air. Is there a solution with GSX to press a BUTTON for request a stair?
If SODE is unavailable for some reason ( crashed, not installed, etc. ), GSX cannot transform a jetway gate with a non-jetway gate, otherwise you explicitly create a customization file for this airport and tell there's no jetway there, but of course it would be wrong to do this, just because for some reason SODE didn't work so, you must try to find the reason why SODE didn't work there.
I assume you are referring to an airport that comes with its own SODE jetways ?