The original request was for ability to compare two different images.- not different versions of the same image.
The reference you point us to does not (in so far as I can tell) document a means of doing that - - Am I missing something?
Note: It is possible, of course, to move back-and-forwards between 2 images in PL’s Full-Screen Viewer - - but that’s never fast enough on my environment for critical analysis of two images. For this purpose, I use a dedicated image-viewer application … such as Irfan (excellent & free) or Fast Raw Viewer (excellent but not free).
Regards, John M