/u/StopReadinMyUsername on reddit created a list called "1001 'GREATEST' MOVIES OF ALL TIME" in 2015.
Since this list is still very popular, he posted an updated list on reddit in April 2020.
For this list he combined the average scores from IMDb, Letterboxd, Rotten Tomatoes & Metacritic, and tweaked the results with data from Letterboxd, iCheckMovies, TSPDT?, TMDb and IMDb.
source: https://www.reddit.com/r/movies/comments/fswg60/by_combining_the_average_scores_from_imdb/