I opened a certain folder with photos. I was surprised to see that the thumbnails were printed with exif information on their entire surface. I did all sorts of weird things to get the thumbnails back to looking right, but to no avail. I finally opened the folder in Windows and saw that each arw file had a *arw.xmp file (correct) and a *.txt file (completely incorrect, because I certainly didn’t consciously create these txt files).
It was this txt file that contained exif information about each arw file and it was its presence that caused this “overprint”.
I deleted the txt files and everything looks fine.
Which version of dt do you use ?
I remember there was a functionality like you describe some time ago (overlay of text from corresponding .txt file). As far as I remember this has been removed some time ago (but I’m not sure). So I guess you are using a (very) old version of dt?
Latest Windows insider 4.5.0-787
It is absolutely certain that this feature was not removed.
It is difficult to say how they appeared and who created them: you yourself, but already forgot about it, or someone gave you these images together with text files. darktable does not create them, it only uses them.