There is often no simple way to unfollow a series or movie. Sometimes you can hide a series but it has to be in a certain place and it’s not universal, including within the app.
It would be great if we moved to a simple follow/unfollow/not following status, where unfollow is an active choice, and no follow might simply be a null value. Unfollow would prevent the system from refollowing a series if you watch an episode again. Not following would be more of a status that indicates there has been no interaction with the series.