No, the EFile extension cannot save / read to / from the Private dir, neither with Companion nor with the APK.
Both yellow marked blocks save in the same dir (→ ASD).
Only the File component can save / read to / from the Private dir:
/data/user/0/io.makeroid.companion/files/test2.txt
But for File component (mistakenly) WRITE_/READ_EXTERNAL permissions are required.
See also here:
The extension developer (vknow360) is aware of this because I pointed it out to him.
He told me, that he will add this method (save / read to / from Private dir) later …
