Windows users have been complaining about a problem with the search box for months. There was even an out of band cumulative update (archive.is) offered for it in January 2020. I thought that this was the search box in Windows Explorer but it's not.
The search box in question is the one that shows up on the taskbar. That's one of the first things that I disable on a Windows 10 installation.
So I turned it back on and looked to see what build I had.
Since I'm not using it I wasn't familiar with the various build numbers.
The point here is that Microsoft is capable and is, in fact, updating the build of Windows Search over the Internet WITHOUT notification nor interaction. Read this Computerworld article (archive.is) about the details. And there's more here (archive.is) with examples of dynamic changes.
Folks, that's called "Windows as a Service."
What else is Microsoft updating silently?
That's not what I signed up for.