M4 MacBook Pro menu bar and app display issues with multiple displays

Application and Menu Bar Issues When Using Multiple Displays

This is an odd one. My Menu Bar settings for Automatically Hide and Show Menu Bar are set to Full Screen Only. On an M4 MacBook Pro.

I plugged in my MacBook to a Thunderbolt 3 dock with two displays, and put Music and Safari in Full Screen. On the MacBook itself, those apps would not reveal the menu bar (not sure if it was immediately or after a while). In fact, Music seemed to go black entirely (so the MacBook screen stayed black even when I hit Escape).

The problem persisted when I disconnected the MacBook from the dock. Rebooting fixed the issue (i.e., pushing the mouse to the top of the screen showed the menu bar for Music and Safari in Full Screen.

I just reconnected to the (hardware) dock. Safari was in full screen on one external monitor. I used the "windows" F3 key to move it back to the MacBook display, and it's behaving properly there now, but now the vacated external display is all black. If I hit F3, that display shows a thumbnail of the desktop in the top band. If I click that thumbnail, the external screen goes black again except for the mouse pointer. Swipe left/right doesn't do anything. It looks like nothing has the focus on that screen. If I give that screen another desktop ("Desktop 2") after hitting F3, I finally get something to look at and swiping works.

Weird.