The Shape of Water is the first Best Picture winner since Terms of Endearment (1983) to not have a male lead
I was thinking about how The Shape of Water is the first Best Picture winner since Million Dollar Baby to have a female lead, but I then realized that it's been even longer since a film without a male lead has won Best Picture. Clint Eastwood was a co-lead in Million Dollar Baby, Kevin Spacey was more of a lead than Annette Bening was in American Beauty, Joseph Fiennes was a co-lead in Shakespeare in Love, Leonardo DiCaprio was a co-lead in Titanic, Ralph Fiennes was a co-lead in The English Patient, Anthony Hopkins was arguably a co-lead in Silence of the Lambs, and Morgan Freeman was a co-lead in Driving Miss Daisy. The last film without a male lead to win Best Picture was Terms of Endearment, and 34 years passed without a movie without a male lead winning again.
Edit: And I forgot to mention, Richard Gere is arguably a co-lead in Chicago.
Edit 2: And I forgot to mention that Robert Redford is a co-lead in Out of Africa