Lightroom Classic 7.3.1 Automatically Write Metadata Changes into XMP "Quit / Cancel

Why don’t you make a catalog backup each time you quit Lightroom. That is a much better safeguard against accidental delete of images. XMP files do not contain a lot of catalog stuff, such as membership of collections, virtual copies, stacks, books, etc.

Great point!

"Automatically Write Metadata Changes into XMP "Quit / Cancel"  Lightroom is still writing changes.  What's up with that?  Is it still actually writing changes?  It's taking a very long time.  Is there a way I can tell if it is writing new XMP files?"

If you see that message, LR is indeed still writing changes back to the .xmp sidecars (for raws) or the files themselves (for non-raws).  It's safe to quit LR -- it will resume where it left off when you restart it.  

You get the most protection by backing up your catalog on exit and by setting the option Automatically Write Changes Into XMP. 

When you accidentally delete some photos, you can recover your edits and metadata changes quickly simply be reimporting the photos. If you didn't have the option selected, you'd have two inferior choices: Either lose the edits to those accidentally deleted photos, or go back to your last catalog backup, losing all the work you've done since then.

When you reimport the photos, you won't recover stacking, collections, etc. but often that's easy to reconstruct, and it's preferable to going back to your last catalog backup and losing all subsequent work.

"When you accidentally delete some photos, you can recover your edits and metadata changes quickly simply be reimporting the photos. If you didn't have the option selected, you'd have two inferior choices: Either lose the edits to those accidentally deleted photos, or go back to your last catalog backup, losing all the work you've done since then."

Not necessarily. You could also open the backup catalog (but not replace your current catalog with it), select the deleted images, save these as a temporary catalog, and then use 'Import from another catalog' to import these again in your main catalog. Granted, a bit more work, but that way you won't lose anything.