Cubase 10.0 works fine with that card. So it’s definitely a Cubase 10.5 specific issue. I downloaded the developer beta of OSX15.6 and the same issue happened. Call me a pessimist, but I wouldn’t expect it get fixed until Cubase 11. I returned my Mac Pro with the 5700 and swapped it for the 580x graphics card. Cubase 10 and 10.5 run perfectly fine so far.