No write access to external micro SD card

I have a x86 tablet where I installed [Android x86](https://www.android-x86.org/). I know this is a rater unusual setup, but I don't think the issue is related to this since other apps on the same system do not have this issues to write to the external micro SD card.

**Issue**
The Android nextcloud client `3.10.1` has no write access to the external micro SD card. The easiest way to prove this is by trying to upload a file to nextcloud. The app then shows a warning that the file system is read only:

Notes:
* The app has all permissions!
* The app never asked me for write permissions on the external micro SD card!

P.S. The bug originally was reported in https://github.com/nextcloud/desktop/issues/1840