Beau is Afraid was the last one I recall. I think it was mostly the latter half of the movie where I started to get a bit confused and needed the ending explained to me.
What movies made you look up some kind of explanation afterwards? I feel like I have done it several times in the past for more surreal movies but can’t think of any other examples.
It can also be a TV show.
I absolutely love 2001 and could not get through Solaris, I’m sure I will try again, but Solaris takes the long meandering scenes (which I generally enjoy) of doing nothing to an extreme, and I say that as a tarkovsky fan as well.
That being said, the third act of 2001 could use a bit of editing for modern tastes.