Using LineageOS on the FP2

@darioce thanks for your recap…
Unfortunately I am not quite there, where I want to be, I tried all your hints with the following - negative - result:

  1. Thats clear and I checked.
  • But e.g. The App SyncMe Wireless has only read access to ext. SD Card, and in Privacy Guard no “Access Media & Photos” is available (only “Notifications”, “Keep active”, “keep in background”, “start at boot”).
    • Edit1a: For SyncMe I read, that there is a beta version, which should be granting write access to ext. SD cards (I don’t yet know, how it will do it. I E-Mailed the devs and wait for the app, as suggested here.)
    • Edit1b: The developer in deed sent me a beta-version of “SyncMe Wireless” which includes a special dialogue in settings to get SD Write acces (and also to withdraw it) and with this it works!
  • For TitaniumBackup also no “Access Media & Photos” is available there.
    • Edit2: TB can access folders, which the programm itself created using option “DocumentProvider” in “Choose folder” options dialogue of TB. Found here.
  • Just a thought: Could it be, that these (maybe outdated) Apps have problems to make a proper request to Android in its preferred way, that they want to access to the ext. SD card? So Android could not allow it explicitley because it even don’t know? And just “grabbing” the permission by breaking the Android rules seems not possible?! But I also want to be able also to use older Apps, not explicitely designed for Android7…
  • It was not activated, but also after activation and after reboot there is no change
  • Unfortunately the structure of my platform.xml seems different from Android5/6 and there is none of the <group gid="sdcard_r" /> entries mentioned there, and a lengthy explanation which I don’t understand:

[details=Details of comment in platform.xml] These are permissions that were mapped to gids but we need
to keep them here until an upgrade from L to the current
version is to be supported. These permissions are built-in
and in L were not stored in packages.xml as a result if they
are not defined here while parsing packages.xml we would
ignore these permissions being granted to apps and not
propagate the granted state. From N we are storing the
built-in permissions in packages.xml as the saved storage
is negligible (one tag with the permission) compared to
the fragility as one can remove a built-in permission which
no longer needs to be mapped to gids and break grant propagation.[/details]
<permission name="android.permission.READ_EXTERNAL_STORAGE" /> <permission name="android.permission.WRITE_EXTERNAL_STORAGE" />

So - any other ideas for granting write access to erxternal SD Cards in LineageOS14.1@FP2 for all apps??