The Mill and the Cross is one of the best biopics about a painter — or, for that matter, any artist — because it concerns itself less with the painter and more with his work; that is, it knows that the 'what' and 'how' matter more than the 'who.'
That’s not to say that the creator doesn’t count for anything; what I mean is that the every artist’s autobiography is recorded in their work (and that’s is why, as I always say, we can learn more about Elton John or Freddie Mercury by listening to Rocketman and Bohemian Rhapsody than by watching Rocketman and Bohemian Rhapsody).