Catalina Finder: Show all windows as default behavior Being a Mac user since 1988, I am used to seeing several Finder windows open and dragging files between them. With the update to Catalina, switching to the Finder will only shown one window, regardless of the number of previously opened windows. Every time I now have to use the menu command to show all windows. That is slowing me down and a poor UI choice.

Now I wonder why there is no setting to show all windows per default. Note this question is not for a keyboard shortcut to show all windows (like in this answer) but for setting the Finder default to the correct behavior. Show all windows, right after command-tabbing to the Finder.
This is not the behaviour that I see (in 10.15.3), so I suspect the cause is likely to be some user settings, either for the Finder, or Mission Control.

The easiest way to check that a problem is cause by user settings is to create another user account, login there, and test the problem. If the problem does not occur in the fresh user account, then you know it's something in the original account's Library.

You could try deleting files from /Library/Preferences that seem relevant, like com.apple.finder.plist and com.apple.spaces.plist, com.apple.systempreferences.plist, and then restarting.

Note that you will obviously lose other parameters when doing this. If removing these files doesn't fix anything, you may wish to restore the old files.