I’d like to be able to scroll down simultaneously, so I can easily copy changes from one document to another
I’m trying to copy and incorporate the redlined edits from two separately redlined documents that were redlined from the same original document.
You can merge the changes into one document.
See: Merging modified documents in the Writer 5.4 Guide
https://wiki.documentfoundation.org/images/0/0d/WG54-WriterGuideLO.pdf#page=77
If this solves your issue, please check the checkbox at left.
If you use Windows, you can use the Snap. With the two versions open, hit the Windows key (flying flag thing) and the right or left arrow. One of the documents will go to that side of the screen. The other will be presented in the empty space. Click it and it will fill it in. Both windows are automatically resized to fit. You may have to use the zoom to be able to see all the text, though. You can also do the Win key and the up or down arrow. That might fit them into the screen better.