If I mark a library or playlist from my Plex server as a favourite it replaces the link to my Plex share on the files screen with them instead of adding them next to the link that was already there.
Before adding a favourite:
After adding a favourite:
I’m on the latest version of Infuse at the moment, version 6.4.2.
Edit: updated to 6.4.3 and it is still the same.