The SSH plugin that KOReader ships requires a patched dropbear(also shipped). It is currently supported for Kindles, Kobos and Cervantes.
Adding support for other platforms is out of scope. There're better ways to achieve the same with an external binary.
In the case of android you can use
https://f-droid.org/en/packages/org.galexander.sshd/.
rsync and rclone are other good alternatives to sync files across devices.