Welcome back and no need to apologize. So I just did the dir /aL /s C:\ as well as dir /aL /s D:\. There were a lot of junctions listed when I did it on C:\ as expected but nothing that jumped out or looked like it linked the the D:\ drive. There were no junctions listed when I ran the command on the D:\.
So I would guess that this is not it. No harm, no foul.
I do not think there is a mirror between D:\ and my Videos folder. I think that whatever mistake I made before, by "moving" C:\Users\...\Videos to D:\ instead of D:\Videos. This screwed things up and I'm not sure why. Because I clicked to merge everything, the D:\ drive now shows once normally (listed as DATA (D) and then once as D:\ with the icon of my Videos folder. These are both under "This PC" in File Explorer. Clicking on the properties for either iteration of the D: drive shows that the default location is is C:\Users\...\Videos, which should not be the case.
Also, I did restore the Original Videos folder using a .bat file from another thread on the Tenforums.