It's IMHO poorly documented (in terms of visibility).
Since it is not enabled by default, you have to edit your config file with the '[sharing]' section. There are two types, by map and token to conform to different usecases. There are also two different storage types, csv and files. Personally i chose map and csv way.
After adding your config and restarting the server, in the gui you can find a new button to share next to your calendar / carddav and in the bottom right menu an entry to accept invites issued by others.
I previously shared with the symlink too but since this update i got rid of it and used this new system and, well, it works for me (i'm sharing ro only calendar but you can assing [limited] permissions too).