FWIW, Likebooks seem to work fine with KOReader. My suggestion would be:
a) Format the sdcard as the internal partition and have read&write access from KOReader
b) Get another app that was specifically built for Android and deals with the SAF nonsense. There're thousands of them
Read-only mode on external storage could be a PITA if you're the kind of person that moves files often or want to store highlights directly inside a PDF. For casual reading it is absolutely OK and the missing metadata you experience cannot be explained by the lack of write permissions.