I’d love to be able to toggle in between photos instead of having to go back to the main collection every time. If there’s a way to do it and I am just missing it please let me know! But sometimes I’d like to go back and forth to compare photos, so that’s a possible feature that you could include.
In general, viewing multiple items at the same time is something we would like to support going forward.
In the meantime, you can use keyboard shortcuts to go to next or previous item in the current view using the keyboard Alt/Option + Arrow Up/Down (Left/RIght would select the next/prev photo in the current item).