I have a late 2013 iMac (macOS Catalina, 10.15.7) with an external DELL monitor (original DELL VGA cable on original Apple VGA adapter).
Since September Adobe CC apps started to behave strange. Usually I open an app (i.e. Illustrator) and sometimes I change the screen, to test colors or because I'm in a call and need to reorganize my space.
When the app is in the secondary screen, when I start zoom in, it simply moves the app to the iMac main screen.
I tried reinstall de apps and the problem persists. Didn't tried to reinstall Adobe CC yet.
I just can't find anything on Google, so I guess that this is not a common issue.