Because you can only watch It's a Wonderful Life and Miracle on 34th Street so many times.
In rough chronological order. For brevity and clarity, I'm mostly ignoring cult favorites that - while bizarre - are still basically trite, family-oriented Christmas fare (e.g., Santa Claus Conquers the Martians, René Cardona's Santa Claus, Santa Claus and the Ice Cream Bunny). Also, note that some of the films listed here may not take place entirely during the holiday season, but instead open around Christmastime, build to a Christmas ending, etc. (A few of them double as New Year's Eve movies, too.) Christmas must be part of the movie's in-universe plot and/or setting; having a Christmas release date doesn't count.
Documentaries excluded because they have no Letterboxd pages as of yet: Christmas With Dad, The Worst Christmas Jobs in History, Wood of Value.