Sorry for long delay – I understand the error, but to investigate and reliably fix I need an access to macOS with different screen settings. I’m looking how to organize it, it takes a while 
For what it’s worth, it works correctly for me with my current (and single) monitor OK. But I cannot test with second monitor, or a different monitor – because the macOS I use is a remote machine provided by https://www.macstadium.com/ . It’s a great way to use mac (and share it with a team, see old blog post about it ), it has served us well… but the limitation is that I don’t really have a physical mac, I cannot swap monitors to which it is connected.
Below is a screenshot how it – correctly – looks for me.
I will get back to this thread once I managed to reproduce and fix the scaling problem, have patience with me please (And if you’d like to help, the hint is that the bug is most likely inside Cocoa + TCastleWindow code, in file castle-engine/src/window/castlewindow_cocoa.inc at master · castle-engine/castle-engine · GitHub . We most likely miss scaling there by some per-monitor value.)
