Yes, the fileformat is perfectly transferrable between PC and Mac. Just make sure you get all the libraries too with it. Only culprit that comes to my mind are the special characters used between the two platforms. : and /. You can't use those within filenames if you want it all to be compatible between the two OS'es. Other than that, no problem at all. We are a mixed OS office and need to transfer projects between OS'es from time to time. I personally use both WIN10 and MacOS daily with Archicad.
OffTopic: Now if only we had relative file paths for libraries, I would be a happy man, because I would not have to point all my libraries again everytime I change platform, or when one of my coworkers need to open and save my file on a different OS than I created it. This happens from time to time too.
AC25, Rhino6/7+Grasshopper, TwinMotion • Mac Pro 6,1 E5-1650v2-3,5GHz/128GB/eGPU:6800XT/11.6.5 • HP Z4/Xeon W-2195/256GB/RX6800XT/W10ProWS