The masks that Big Daddy (Peter Serafinowicz) and his gang use to hide their identity are of Snowball from The Secret Life of Pets (2016).
In both Sing and Sing 2, Ash (voiced by Scarlett Johanson) comes out near the end, in both cases she has to perform acapella at first in order to whip the audience up for the finale.
The scene where Scarlett Johansson's character argues with a venue owner for underpaying her for her performance has a parallel to Johansson's legal conflict in 2021 with the Walt Disney Company when she complained that the company underpaid her concerning the theatrical release of the film, Black Widow (2021).
The film was released in theaters 1 day after the first movie's fifth anniversary.