First, no storage access permission is asked. Ok, set it manually. Now:

On A7: double extension appended to the backup file .darkmxconfig.darkmxconfig

On A11: Still throws the error:
"Error opening file for export:
Operation not permitted (1)"

I'll get this fixed up, at least the double-file extension problem.

When you say you manually turned on storage permissions, do you mean the "manage all files" permission?

DarkMX uses Storage Access Framework everywhere, so permissions beyond the folder/file specific ones that come from the file picker shouldn't be needed.  In the manifest, I did put READ_EXTERNAL_STORAGE WRITE_EXTERNAL_STORAGE but those don't do anything in A10 or newer IIRC.

I'll check into this more closely before the next release (very soon) but in the meantime if you can give me more details it might save some time.

I mean the only permission ('Files and media' on A11) for the app that aren't enabled on first app run nor on first access of directory chooser UI (via Android Settings menu). On A11 the system AOSP/LOS dialog shows up fine and allows a directory selection but after pressing OK button it throws this error. Every time the backup file written with size 0. BTW the double file extension is only on A7 which works after enabled the permission.