Thank you for reporting your issue!
Unfortunately, I can't reproduce it, are you sure you're using the latest version of the app?
1. my predicted movies now show -- as what I like best -- movies rated "not interested+"
Where does it show that? I've tried the interface, I've tried the export, but I don't see that.
2. can something be added that explains what happens if you mark a movie as one that you are not interested in?
You're right, I need to add a section to the help page (in fact, I was convinced that there was already one).
A movie you mark as "not interested" won't be listed as "predicted". It's a way to clean your list of recommendations.
In the case of a series, you can mark it as "not interested" even if you've already rated it. That'll remind you that you don't want to watch more episodes from that series.