I have the same issue - it seems Apple and AMD need to update their drivers for the Apple AMD cards (you can only download those drivers from the AMD website - the other more recent drivers won't recognise your hardware. So the only solution is to beg/pester Apple to update their AMD drivers.
One other solution, which I tried (and it works), is to go to www.bootcampdrivers.com and they have the latest AMD drivers for October (I think its called AMD October RED) which work specifically for Apple BootCamp, but this is not supported by Apple. So try at your own risk. It worked for me, and I played the game...but I later uninstalled and went back to the official Apple drivers and want to keep my system stable… but Squadrons doesn't work again in BootCamp.