I'll try to be clearer.
I have always installed iGo Nextgen without problems on the Main Memory and the Maps on the external SD. With this configuration, in the SYS.txt I gave these instructions:
has_secondary_root=1
android_secondary_root_path="/storage/40FB-A3B3/addons" ; where the content/map folders are in Addons;
With this configuration I can only use one type of Map at a time (TomTom or HERE), i.e. I cannot switch between TomTom or HERE and this configuration works both on Huawei P9 (Android 8/9) and on Oppo Reno8 5G Android 13.
This means that access to the Root of the SD and its Main Folders is always guaranteed, both on Android 8/9 and on Android 13.

In order to use the two types of TomTom and HERE maps at the same time, I followed this tutorial on OPTION 3:
[Only registered and activated users can see links. ]
With this configuration, in the SYS.txt I gave these instructions:
has_secondary_root=1
android_secondary_root_path="/storage/40FB-A3B3/Android/data/com.gja.nav.utility/files/addons"
This configuration on the old Huawei P9 (Android 8/9) worked perfectly, but it no longer works on Oppo Reno8 5G Android 13 which returns the Error: Maps not found (Unable to access Maps). This means that Android 13 prevents access to Folder com.gja.nav.utility according to the path /storage/40FB-A3B3/Android/data/com.gja.nav.utility. This path should be reachable via SYS.txt instructions and used by the Map Changer app.
Confirmation of my observation is also found when I try to access this Folder with the File Explorer of my smartphone which returns the Error: Loading Error - Access Denied.

Spoiler: Error
[Only registered and activated users can see links. ]
[Only registered and activated users can see links. ]


Even the creation of the com.gja.nav.utility folder itself must be done via the PC with the oTG function of the smartphone, i.e. it is not possible to create the com.gja.nav.utility folder directly on the smartphone via File Explorer.
App access has been guaranteed.
Spoiler: Permissions
[Only registered and activated users can see links. ]

Sorry for the length of the post.