Back in 2012 a couple folks asked for this feature so I'm just gonna quote @jpu here:
jpu Dec 1, 2012
I have found this feature useful in another file manager - the ability to lock the viewer pane to the currently selected file so that it remains unchanged regardless of which other file(s) I navigate to/click on.
It could be shown as a padlock icon with tooltip ‘Lock/unlock the current file in the viewer pane’
None of the developers replied so I guess it just was eventually forgotten.
I have a very long image of a file list that needed to be scrolled about as reference while working around in dual or commander view mode. Clicking and navigating around other files constantly changes/refreshes the viewer pane -- always loading the next file selected. It would be very useful to be able to temporarily 'lock' this pane. Of course, I've also tried the alternative workaround of just opening another standalone viewer pane window. However, I think that this is a very useful feature not just for navigating images or working around an image reference, but also for documents as well -- it takes a while to load individual previews of documents, and sometimes it's useful temporarily lock this pane rather than toggling it away just to be able to click on or navigate around another file or folder.