Sorry for the delay. I’ve been away from my computer for a few days and I just saw your other post a little bit ago, so I fired up my laptop to make the app copyable again. Now you can make a copy so you can take a look at it.
The quick version is that I have the MemoryDetails sheet which holds all of the submitted images by users. Then I have a MemoryDetailsLookup sheet which takes those rows and compresses them without spaces and I then add navigate columns which determine the previous and next row ids. Those values are then pulled back into the original MemoryDetails sheet so it can be used in the app. Those navigate columns become an array that I can use to create a relation for the inline list that I use as navigate buttons in the app. I also have a formula to assign row numbers, but I don’t think I’m doing anything with that at the moment. This is a pretty old app and I haven’t touched it in a long time. Now I would probably approach it differently and try to accomplish it only within glide, but I’d have to spend some time to work that out.