Answer
The library's streaming film database, Kanopy, requires users to authenticate by logging in to Kanopy through the library in order to stream a video.
When you share your screen in Zoom to share a video with your class, you are the only person who has been authenticated by Kanopy, so everyone else only sees a blank screen instead of the film.
Instead of sharing your screen through Zoom, you can send out a link to the video you would like everyone to watch and ask them to watch on their own. Then everyone can meet over zoom after watching to discuss.
If the film is available at Tubitv.com, you can share your screen through Zoom IF YOU FIRST SIGN-IN TO TUBI.
(Tubi will show ads if you are not using an adblocker on your browser.)