I tried this command:
adb backup -apk -obb -shared -all -system
It seems to start but then it stops at about 4 GB (from about 9.5 GB occupied storage - from 11.6 GB initially available). The display of phone shows "shared storage" and there's no further progress since more than one hour. So I don't know how do I get this backup done.
The worst example of app which hides data from me, even though it's my smartphone is built-in Internet Browser. Over time I got 2.9 GB of saved pages which I can't access without root. Now I have no way to access my data and smartphone is nearly useless without sufficient storage.
How do I extract this hidden data? From all apps or at least from this Internet Browser? Thank you very much for your answers!