CC: Problem to change folder in MIUI8

Hi folks!
I have an RedMi Note 2 with MiUI 8 global, 7.4.20 Beta (language: German).
On this I work with CC 5.2.5.2 (359).
I send all menue-items and messages "as I do read them" - most in german.

I want to change the default folder (to the SD-Card).
I do the tree dots, "Einstellungen", "Buchformate und Speicherordner", "Standardordner".
I get "Wähle einen neuen Speicherordner ..." and select "Wähle einen Ordner".
After this a message appears "Android 5+ folder chooser ..." with english text and german texted choice links. My choice is "Fortsetzen".

After this, the problem start.
I get first the message "Aktiviere zuerst Dokumente unter Einstellungen > Installierte Apps" and then "No folder was selected". :blink:

I can find in my Miui-"Einstellungen" the point of the installed apps,but I can't find the point "Dokumente" there. :chinscratch:

In other apps, I can change the default folder without problems (for example moonreader or amazon kindle) on this phone.
On my lenovo-tablet with android 6 I can do so with CC to.

Who can give a tipp or help, where to search (in permissions I can't find "Dokumente"...) or how to do ot whats wrong? :chinscratch:

For this I thank you in advance!

And thanks to the developers for this great app!
It's working fine on my tablet!

Ciao
Fomtom