Cannot drag apps to monitor

<< I don’t think I want to try that “spaces” thing because it seems a bit complicated. >>

Can you see how the Mac CAN treat both displays together as one larger Extended Desktop?

If that makes sense to you, turn OFF "Displays have Separate Spaces".

Then make certain your displays are oriented in the arrangement pane) the same way as the physical displays are oriented on your bench (if not, drag the blue boxes around until they are.)

Then the mouse can move freely between displays, and can carry a window with it.

There are Two COMPLETELY DIFFERENT ways of working with Multiple displays.

The default is to use Extended Desktop to concatenate a second display along any edge of your existing display, which simply increases the size of your ONE desktop. Then you can drag windows (but NOT Applications) anywhere you like on that larger desktop. You can even leave a window half on each display, and when you scroll, the two fractions will be updated "the right way".

The second [in my opinion] harder to set up is called "Spaces" only makes sense if you have already been using Mission Control to provide an iPhone-like Home Screen with App icons on it. An extension of mission control is called [multiple] "Separate Spaces", where ONE display can have any one of several pre-configured "Spaces" (with specific Apps attached, if desired). "Spaces" can then be swapped onto the ONE display when required.

"Displays have Separate Spaces" is a generalization the "Spaces" concept onto multiple displays. Each SET of "Spaces" is connected to only ONE display.

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At the most fundamental level, you may need to enable/disable "Displays have Separate Spaces" feature to get all of this to start working the way you want.

the setting used to be here, but may have moved slightly in current versions of MacOS:

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The built-in display should NOT go black when you start to put things on an external display. Both should be working at the same time. Something is wrong with that.

lets go down the list:

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are you running anything like that?

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