If you are looking for the subtitles of this movie "One Flew Over the Cuckoo’s Nest" then I will suggest you check subwhale.
I have tried few sites but all they have are ads and some pop-ups.
Subwhale.com does not have any ads or anything at all on them. You can check them for any movie subtitles.
One Flew Over the Cuckoo’s Nest Movie Subtitles from Subwhale here: https://subwhale.com/movies/one-flew-over-the-cuckoos-nest/