On my Dell 34 monitor the latest Photoshop 21.2 (Mac OS 10.15.5 Catalina) has a serious issue. It won't refresh screen if you make changes. The screen just go to dark grey as soon as you make changes in art boards. Then if you move the art board it'll go back to normal. This happens consistently when you have many art boards in one PSD file. Downgrading to 21.1.3 solved the issue completely.