I found the problem
I'd noticed that the S10 had some .nomedia files in some libraries, (note the S9 does not although it is running the same version - Android 9.0
One of these .nomedia files was in the Root folder of internal storage. Didn't know what they were for so Googled it - they are used to speed up scanning for media files - i.e. if a .nomedia file is in a folder it will not be scanned , including any subfolders.
Why it was in the root I have no idea, but once I removed it, the files in Notifications became available.
Weird thing is it somehow didn't affect the Ringtones folder, Music folders etc.
I found another 9 on the phone, all in folders that don't or would not have media, mostly in the Android folder.
Any way, problem solved, and this might help others.