P: Constantly "saving xmp for xx photos" slowing down my Lightroom Classic!

After watching Junction10photo's video showing excess XMP activity, I realized I was experiencing the same thing -- mainly because I had seen performance deterioration with LrC 13.5 and 13.5.1 that I hadn't seen previously. 

I wanted to see if I could reproduce the problem intentionally. Here's what I came up with, and now I can repeat it at will. 

I have "Automatically write changes into XMP" turned on. I'm not synching any collections to the cloud.

I have a collection with 25 images in it; the images are only in this one collection.

In the Develop module, I first right-click on one of the images and select "Show in Finder" then filter the Finder list by ".xmp" and sort it by descending Date Modified. This is so I can easily see what happens next.  

I select 15 of the 25 images, turn on Auto Sync and make a basic editing change. All the XMPs for the images I just edited get updated, with their Date Modified set to, for example, "Today at 10:55 AM." This is expected, of course; and I used Auto Sync simply to get the same Date Modified on all 15 XMPs.

Without doing anything else in Lightroom, I wait until the computer clock changes to 10:56 AM.

When the clock changes, I switch from Develop to Library. After a few seconds, the 15 XMPs get updated again, with their Date Modified changed to "Today at 10:56 AM" -- even though I didn't make any more changes to them after the Auto-Sync/edit.

I wait another minute (for the clock to change) while in Library view without doing anything, then switch back from Library to Develop. All the same XMPs are updated again, their Date Modified changing to "Today at 10:57 AM."

I keep doing this, and every time I wait a bit and switch between the two modules, the XMPs get updated. This isn't the only time it happens; it was just easier to explain this way with a repeatable test. It will also happen if I stay in Develop and edit images; select different ones; switch between collections; pass the mouse over the filmstrip; or leave Lightroom open, work in another app, then return to Lightroom. These last two are weirdly fascinating.

Here are some other observations on what else may be happening because of these extra XMP updates:

- Memory usage climbs substantially, when the only thing I do is switch between modules. Performance drops, and the memory isn't freed until I restart Lightroom.

- I often get the "Adobe Lightroom is not finished writing metadata changes..." message when exiting -- something I had never seen until I updated to 13.5 then 13.5.1.

- I had been syncing about 500 photos to the cloud until recently, but noticed (by watching Sync Activity in Preferences) that sync kept looping repeatedly through photos it had already synced (and I hadn't edited). I reset preferences and followed the reinstall procedure for Lightroom, but the problem persisted so I stopped synching. Now I wonder if repeated syncs were getting triggered because of the excess XMP updates.

In conclusion: Well, I can't really think of anything, but maybe this testing provides some insights into a number of problems people are reporting since the 13x releases. 

A full-resolution screen recording of the entire LR window could also give more clues and understanding.

Can you [post a screenshot of your LrC /Catalog Settings/Metadata/