How to access arbitrary path on SD Card

Hi all,

I've been searching everywhere to find my mistake or the problem.

My goal:

Let the user pick a folder on the phones SD card to store data in this folder.

Problems:

I am able to let the user pick a folder but I always get an Unauthorized Access Exception, despite having the read/write external access permission. I can write to my apps folder in the internal and external storage and I am also able to write to an arbitrary path in the internal storage.

I receive a path like the following: /storage/fe23-fwe3/MyFolder, where fe23-fwe3 is my specific SD card.

I try to access the folder using PCLStorage package. This works totally fine when using it on Windows (UWP)

I've been searching for an answer for more than a week now so I'd be super thankful for some hints!