Searching for a movie that I don’t have in my library, “Dazed and Confused,” for example, will show up with my admin user, but it does not show up when I try to search with my regular users. I can’t seem to find any settings that would turn this feature on for the regular users.
I’m also noticing this limitation extends to adding reviews and managing watch lists for each user.
By “regular users” are you referring to managed users in Plex? If so, check this page and ensure that the features to which you’d like them to have access are not set to “Disabled for managed users” but “Enabled” instead.
https://app.plex.tv/desktop/#!/settings/online-media-sources
The discover features/function is not available for managed users on your account, if that’s what you are referring to. A workaround is to create separate plex accounts for each user and then add them to your Plex Home.
There’s a feature request to enable the functionality: Add Discover to managed users
