My browser / operating system: MacOS Macintosh X 10.15.6, Safari 13.1.2, No Flash version detected

I installed Scratch 3.12 on my MacBook and have the problem that the stage area seems to be blank. It isn't, when I click around with the mouse I can catch objects and they get visible in that moment. When I release the mouse the objects disappear. I re installed Scratch, I downloaded Chrome and made it standard but no solution…

Has someone more Ideas ? My boys get desperate and me getting too…

This happened on another one of our computers running Firefox, the stage area (a.k.a. player) appeared as a black box. Is this your problem? If so, using Google Chrome may fix the issue.