White Box appear on the lefthand corner of computer screen or on the left hand corner of the 2nd screen

I am seeing this same issue. Added details:

• By default this dialog seems to appear on whichever screen is the "Main display" in the (revamped-for-Monterey) Displays System Setting.
  • When I booted up immediately after installing Monterey with only the internal screen of my Intel MacBook Pro, I can't be positive whether it was there or not, but I didn't notice it.
  • I usually work with two external LG 27UL500 monitors. When I have one of my 2 external monitors set as the Main display, I can't seem to make this appear on my internal screen at all -- even when I disconnect the two external monitors and use only the internal one.
  • However, if I assign the internal screen as the Main display, the dialog appears by default on the internal screen.
• The heading of the dialog is just "---" as in the original comment's screen shot.
• The dialog cannot be moved by dragging the title bar. It doesn't Drag.
• The Close button is styled as if it is disabled -- but clicking it results in exactly the same behavior as if I click Check.
• The Check button is enabled.
• On clicking either button, another dialog just like this one will appear on another external monitor.
  • Clicking Check in that new dialog makes the second one go away again.
  • Clicking check from the internal screen, I get:
    • First click: shows the dialog on one of the external monitors.
    • Second click: That second dialog moves (in an animation) to the other external monitor -- but then disappears from the new spot as soon as it arrives.
    • Third click (on the dialog on internal monitor): The animation moves the dialog back from the spot on the second external monitor (where it just had disappeared) to the first external monitor.
    • Subsequent checks (On any spot where the dialog is displayed at the moment): Moves the dialog back and forth between external monitors. It always remains up on the Main monitor.

• The modal here floats in front of most other elements on the screen. I believe Zoom's Participants list is the only thing I've seen over it; other elements (like this Safari window) appear behind the dialog.
• Rebooting doesn't help.

After a couple of days fighting off this dialog, I am now seeing it only intermittently. It currently isn't up on any of my monitors. I have had it go away and return a couple of times.

When it does appear, it's just as obnoxious. For example, last night I went to project an Apple TV purchase from my laptop screen, and the dialog sat above the playing show... You can't watch that.

Some combination of changing the Displays > Main Display setting and rebooting my system seems to address the problem, at least temporarily... today. I think. When one is trying to work, one doesn't always happen to notice the moment it disappears.

Dialog is back this morning as I hook up to my 4k monitors at home.

I seem to have coaxed it to the bottom of the external monitor it's on, and perhaps that explains it not appearing on my smaller, work monitors?

(It doesn't look like I've ever installed the VLC media player app.)