Orphan blank window randomly pops up

Question

Since about a week ago, I've had a window like this one1 popping up out of nowhere a few times a day.

It's not "attached" to any app, in the sense that it's not coming to the foreground while using the app switcher. Selecting it doesn't show a corresponding app name in the menu bar either.

I closed all my apps, then all the menu bar apps, then I opened Activity Monitor, selected everything and then "Quit" and it was still there.

If I close the window, sometimes a new one pops up; sometimes it just goes away and doesn't seem to come back for a while.

Is there a way to find the process that corresponds to a particular window like that?

  System Version:   macOS 12.0.1 (21A559)
  Model Name:   MacBook Air
  Model Identifier: MacBookAir10,1
  Chip: Apple M1
  Total Number of Cores:    8 (4 performance and 4 efficiency)
  Memory:   16 GB
  System Firmware Version:  7429.41.5
  OS Loader Version:    7429.41.5

Answer 1

There's a duplicate on SuperUser explaining your options. These basically are:

• Use the Accessibility Inspector from Xcode. It can show you the app name (you need to enlarge the Accessibility Inspector window or scroll and open the Hierarchy section; the top entry is the app).

• Use the lswin.py script. See the comment on that answer for a Python3 solution.