The Last Christmas (10:35)
IMDb; official website; YouTube

This 2021 short film was presented by Alter in 2023, but I first saw it on Screamfest's YouTube channel in 2022.

Late on Christmas Eve, 8-year-old Alice wakes up her teenage sister, Kirsten, to tell her that she had accidentally killed Santa Claus. She eventually convinces Kirsten that they need to bury the body, but that plan hits a snag, and... I don't want to spoil anything else about the film. But the girls both swear a lot (which is just one of the ways in which Alice seems precocious), and the whole thing is pretty funny and twisted.