To get this right I think you should Save as DWG from the floor plan window, and use Model Space as target. If you save from a Layout you won't get empty layers, I think, at least not if you save to Paper Space.
Please check Archicad's Help file on DWG conversion. It's quite good, better than the manual, but you have to read every word on the operation you're working with. Don't miss a step!
AC4.1-AC26SWE; MacOS13.5.1; MP5,1+MBP16,1