Watch it here:
The Lighthouse (2019) = Shutter Island (2010) + The Shining (1980)
Indeed, The Lighthouse is basically a more artistic version of Shutter Island. A major difference between an artistic and an entertaining version of (more or less) the same movie, is that in the latter the film explains itself in the end, whereas in the former very little (if anything) is explained, and the confused viewer must look for an explanation on the internet.
An explanation like this one, for example: