Contrary to common belief most introverts are okay with certain social outings, including the infamous Christmas dinner and the horrifying (but also adorable) cheek-pinching grandma. But to survive this there are a few things that introverts, especially students, do over holiday breaks to compensate the Christmas cheer they are forced to exude. Just as every person is different, every introvert copes in different ways.
At the Christmas meal, my family often does breakfast over dinner for special occasions; an introvert probably sits there patiently but mildly agitated because they want to get back to their leisure slash coping mechanisms for having to be out among so many people so much. At the table, if an introvert zones out, their thoughts might look something like the following: "Blah blah blah blah blah, [inset family designation i.e. sister, grandpa etc. followed by name] will not shut up. I bet in [title of book series, TV show, movie or video game] there is a spell or something I can do to at least change the topic or silence them, although if we were there this situation likely would not exist...Well, it could be a "yule" holiday in some other universe I suppose, where families gather to ride out the cold winter. I will go to my enchanter's tower and take a silver amulet I was given a while ago and create a 'selective hearing' charm for myself that silences most of my family's incessant talking about meaningless things." In this moment the introvert identifies with either Scrooge or maybe the Grinch. Definitely the Grinch, because we do like Christmas, just not people per say.
While an introvert sits at the dining table waiting for the conversation to go past superficial topics, they are experiencing adventures in their head. Slaying dragons in Skyrim and riding them to war in Westros. Parlaying with an icy witch and a talking lion in a wardrobe. Or any number of other scenarios going on in their head based off of various forms of fiction media.
If you really want to love on an introvert this Christmas, do something not quite as socially involved. Take a movie marathon with them, "Lord of the Rings" and "The Hobbit," or "Harry Potter." If they are a book worm, ask them about it and how they feel, especially if you are never going to read the book or just do not care, tell them to open the spoiler flood-gate. A reader introvert enjoys talking about their books almost as much as they do actually reading them. An introvert's cheer may be a little bit hidden, but we do like Christmas.
"BLAST this Christmas music... it's joyful AND triumphant," The Grinch