Hi,
I have a weird problem, when I try to select a folder for backup/data storage inside an app it opens the system file browser, but there no folders are displayed and only an option to create a new folder, but selecting that creates a new folder that is also not usable.
Other providers (such as the nextcloud) do work, once selected, but I want to store stuff on my primary storage.
Can anybody give me pointers in any direction?
Welcome to the Community Forum. 
You might want to check if you have granted the apps sufficient permissions to access your internal storage. Check Settings > Apps > (whichever app is concerned)
Try clearing the cache of the file-manager app. Did you try to restart the phone yet?
It should not be a permissions issue, since all the affected apps do not request storage permissions, and therefore rely on this (broken) system picker
So far I have tried:
Did not yet uninstall/reset storage for the affected app, since I currently can’t create a app data backup and don’t want to lose the data if at all possible.
Which App?
And which File App do you use? And why not creating a folder and store in this folder?
I need it for the Signal Messenger to store Backups, but it is not the only App affected for me, for example OsmAnd and Kindle Apps also face the same Problem.
The “File” App mentioned above is only named “File” and seems to provide this folder picker.
As mentioned in the original post, the Button “Create Folder” does create a new folder, which I also cannot select and use.
Sorry missed that part.
Do you by any chance have an SD card inserted and formatted as internal extension?
Edit just for clarification: I think the screenshot shows the overall files system and no Filemanager App to display files. So you cant delete cache and storage.
The stock files app is the one from Google.
Just for clarification, this is what you expect to see, right?
Also yes you can get a shortcut for the built in file manager. It will be names “Files” with a blue background and white folder.
(left one is the shortcut I made for it, right one is fossify file manager)
Yes @Furdiburd that is what I expect to see.
In the sidebar also my nextcloud and my terminal emulator show up.
In those folder it has no problem selecting something.
But since my nextcloud instance is only in my homenet it sadly is not a viable backup location and why my terminal emulator shows up, I have no idea.
“It should not be a permissions issue, since all the affected apps do not request storage permissions,”
But photos and videos are allowed right? Also can you download this app to see if your built in file manager is okay?
“Photos and videos” Permission is set to “Always allow all”
When opening the Files app directly it show all the folders as expected.
