Your screen capture shows line #10 to #12, but in order to use this feature with your mouse, you need to scroll to the very top of the document, before line #1:

☛ This feature was first included in Trados Studio 2019.

This was the picture of my screen.

Then being that I was having problems with adding files to my project, when I added a FOLDER instead of an individual document, it asked me I wanted to revert to SDLXLIFF format and then, voilá the screen now includes the square the same as your screen. So, again, thank you for responding.

I am replying to the reply to myself. I spoke too soon. The ability to click on the left of the name is gone again. I tried a different document, but the issue continues. Oh, well.

I am replying to the reply to myself. I spoke too soon. The ability to click on the left of the name is gone again. I tried a different document, but the issue continues. Oh, well.

When I first open a file, that cell in the left corner doesn't show up either, but it does if I scroll up with my mouse or keyboard

Are you sure that the it doesn't come up if you scroll up?

It is sporadic. This is what I just noticed.

Please notice that the beginning of the document does not contain the ‘orange’ name of the document (I am sorry but I do not know what it is called), but it does have the closing ‘orange’ tag at the end of the document.

I would expect that all the documents would start like this one, which contains the open ‘orange’ tag at the beginning and the close ‘orange’ tag at the end.