Answer:
If you open the hall model in RFEM instead of RSTAB (create a copy of the model and change the file extension from *.rs8 to *.rf5), it will be possible to import the support forces after calculating and saving them. To do this, open "Tools" in the model of the floor slab and select "Import Support Reactions as Load".
Then, the support reaction can/must be transferred individually for each load case. The load combinations are then generated as usual in the RFEM program.