How to identify which program has left a portion of its UI floating on my screen?

I noticed that what looks like a tooltip saying “Increase Indent” is floating homeless on my screen. Here it is with the edge of the browser window beneath it:

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It has attained nearly infinite Z-order and sits above anything else I can move around, even Task Manager. (It does not superimpose over the lock screen)

How can I figure out which program owns this, so I can terminate it? I’d prefer to do this in a minimally invasive way – ie, not just reboot.

I have already closed certain applications just by guesswork but didn’t luck into the offender. (Possibly, since this seems to be a bug, closed applications didn’t actually terminate their processes).

Searching for “increase indent” specifically floating like this didn’t turn anything up, but I was hopeful this could be a commonly known issue.

I imagine there could be some utility (built in to Windows, or 3rd party) which might let you click on any UI element and identify its process?