It should work alright if you got iCloud Drive checked in both of your machines: System prefs - iCloud - iCloud Drive. At least it works for me.
I have been using DropBox for years, and it has worked seamlessly and very quickly for me and for my use cases. The only limiting factor has been the internet UL/DL speeds. It has been a time saver for me. Very convenient service.
I have used iCloud Drive too to share documents. Some Apps use it natively, but it should work for any app as well. It has been a little bit slower than DropBox, but it works quite nicely too.
Now I have moved to iCloud option which synchronises the whole document folder and desktop folder of my main machine at home. This way I can access everything from everywhere in my Mac Pro documents and desktop folders if I need to.
Only thing to remember with either service is that you don't want to shut down or put to sleep your machines until all files have been synchronised. That is why I have a sleep timer for most of my machines. I just leave them on all the time, and they sleep when their idle countdown tells them to. I set it to several hours to ensure full file synchronisation.
I have got a win10 machine nowadays too. I have yet to install iCloud drive to that machine, but I have no reason to believe it would not work as expected. I might test Microsoft OneDrive too, and I would expect it to work similarly and as seamlessly as the above mentioned cloud services do.
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