Since I wrote my post above, I found that the File Explorer Count plug-in does not count all the files that Obsidian counts: it counts far less, so even at the top (vault) level, where the Obsidian mobile apps do give a file count, the (accurate) number quoted by Obsidian is a good deal higher than that quoted by FEC (I have therefore edited my previous post to reflect this, and uninstalled FEC.)
What I am trying to do is to find out why the total vault file count on my iPad does not match the total on my other devices. I am using Obsidian Sync and wanted to see if any files are missing on iPad, or duplicated everywhere else. It appears that this exploration will have to wait.