After that, you can show or hide content that’s identical, content that’s different, and/or content that only exists on one side or the other. (I use the Full Contents method when I want a hash comparison of files to verify they’re identical, but that takes a lot longer and isn’t sensible for this use case.) Then in the View menu, make sure to enable Tree View. When you set up the compare, for this you’ll probably just want the “Size and Date Modified” method of identifying differences. There’s a portable version available if you don’t want to install it. I don't know what it's backed up or even if it accounts for the difference, but it seems to be the likely culprit for this size change given a cursory evaluation.

I got a notification from it yesterday after yesterday's morning Full backup that said it had done some kind of file backups.

Just as a preliminary guess, I think it's some kind of file backup that Dell's SupportAssist application does. This time, I will install that application, compare the two mounted image sets as virtual drives, and see what I can find that can account for the difference in image sets. I hate to ask you again, but what is the name of this application? You've mentioned it several times in the past in other posts where I talked about this application, but, once again, I've forgotten what it was sorry for that. You recommended I mount the two different image sets as different virtual drives and using some application you use and recommended to show the difference in the file contents of the 2 drives. Starting today, the difference in backups increased again by about 8 GB. Sunday, I restored down my Windbackup to update it to 20H2.

By dbminter - 5 November 2020 9:10 might remember a topic I posted a year or 2 ago where I encountered a massive increase in my daily image backups.

Winmerge compare entire drive