A Microsoft file hosting and synchronization service.
The registry fix provided by @Ferreira Cédric didn't help.
Manually installing updates in Office only helped a little (https://support.microsoft.com/en-us/office/install-office-updates-2ab296f3-7f03-43a2-8e50-46de917611c5)
I found that when I launch a Word (.docx) file from File Explorer or a terminal (start "My/file.docx"), AutoSave is turned on. When I launch the Word document from Everything (https://www.voidtools.com/), AutoSave isn't turned on. So, that leads me to believe that there is a problem with AutoSave when files are launched using a certain API. Anyone have any ideas about this?