I have exactly the same issue. TV series played from Library shows in "Up Next" but when I go to continue, it diverts me to Paramount +. I have removed paramount+ from the Apple TV and instructed Apple TV not to show Paramount+ shows in the settings, but it still gets hijacked to Paramount+. Try finding the right episode in the library a few seasons in. I cant think of a more useless interface for purchased videos after many loyal years to Apple.
The only solution I can think of is to only buy shows from Amazon Prime. They have the same purchase options but you will be able to continue series and movie watching through either the Amazon Prime app or Up Next, which doesnt get hijacked. Apple definitely dropped the ball on this one and this is a symptom of the post Steve Jobs era. Back then, he would never have accepted such shambles .