Babylon’s ending is divisive for several reasons, but Manny’s emotional reaction to Singin’ In The Rain is actually the perfect conclusion to his story. Babylon follows fictional movie industry figures Manny Torres (Diego Calva), Nellie LaRoy (Margot Robbie), and Jack Conrad (Brad Pitt) through their pre-Hays code Hollywood careers. One of the major turning points of Babylon comes when movies transition from the silent era to talkies, and while this spells the end for Nellie and Jack’s careers, Manny’s career soars in the wake of the change. Despite Manny’s success, he ends up having to leave Hollywood after becoming involved in Nellie’s deadly gambling debt to James McKay (Tobey McGuire).

https://screenrant.com/babylon-manny-crying-singin-in-the-rain-meaning/