Hello,
recently i tried using a 32GB Micro-SD Card from Samsung in a Galaxy S8 on Android 8.0.0 .
My Nextcloud-version is 13.0.5 and my Nextcloud-appversion is 3.2.3 .
The Micro-SD card itself is freshly formatted in ex-fat and i also tried using Fat32 before.
So i opened the settings and tried to change the storage location, but the only locations i can choose are
/storage/emulated/0/Android/media/com.nextcloud.client
/storage/1E7C-5CD3/Android/media/com.nextcloud.client
/data/user/0/com.nextcloud.client/files
and
/storage/emulated/0/Android/data/com.nextcloud.client/files
Then i as i allready set formated it to exfat but with no improvement. My phone itself recognises the sdcard and e.g. saves automatically pictures or videos on it. I can even move most apps to the micro-sd card but this does somehow not work for Nextcloud. In the internal FileExplorer from Samsung itself there is the “internal storage” and the sd-card, so the phone itself recognizes it and uses it seemingly correct. It can move other data on it and even complete apps without hesitation, this simply just does not work for this app. 
Am i missing to give it permission to see the sdcard? I looked i the permission-settings but i did not find anything that gives it extrapermissions.