The X6 is back from the branch office, everything is running again now.
I called the BMW breakdown service hotline in Munich and said that they should not send me a towing service, but the BMW service vehicle, so that a software reset can be carried out. Was rejected and insisted on towing. Towing service No. 1 came and had to give up because the clamp did not reach the rear wheels, because the X6 was too deep in the garage and the winch would have hit the garage door at the top. I called the BMW breakdown service hotline in Munich again, insisted on another towing service, this time the ADAC came and it was found that the X6 can only be pulled out with 4 floor rollers, but the (new) paving of the driveway would be destroyed , therefore not possible. Fortunately, the ADAC Servicemann knew the BMW service mobile driver at the nearest BMW branch (35 km away), who came, reset the software and the engine started again. It still had to be towed (I was able to drive it onto the loading area myself) because the BMW serviceman prohibited me from continuing because the software was only installed in an emergency. After 5 hours in the BMW dealership, the X6 was ready for use again with the software 03.2020 / 31.
Conclusion: I can tell you the next software update where I will do it: directly in the courtyard of the BMW dealership