File Sharing in iTunes for Windows works with old iPhone Pro Max 12, but most folders missing with new Phone

I have a lot of Apps that store local files on my devices, e.g. videos in Media Players, Panoramic images in my Pano viewer, etc.

A little while I back I discovered, when setting up my new iPad 13 Pro, that a lot of these files don't get copied over when you set up a new device from the backup of an old one, so I had to do it manually in iTunes later. (Some did get restored over though!)

Today, when setting up my new iPhone 16 Pro Max, about 80% of the Apps don't appear in iTunes File Sharing (Spotify does, so it's not just Apple apps there), hence I can't copy the files over from my old phone, or my computer (note both phones are running iOS 18.1).

So my question is - how do I get the files (which I've already copied from my old phone to my PC, expecting this issue) into the Apps please? It clearly works with my iTunes version and my old phone.