I wondered whether the practice engendered by a year of pandemic would make the holiday isolation less noticable. Apparently not. This is the time of year when it seems everyone says they are going to spend the day with family. Many actually do. No one says "This year our family has decided to be your family."
I might decline. Many families get together for too long a time and I would probably get bored before it seemed polite to tell them I'd had enough. Many families are also too large, especially on a holiday, which can be distressing for an introverted prosopagnosiac. Lots of people I don't recognize swarming around me is an experience I can remember from when I had a family of my own. (Once I visited some family I had never known holding a feast celebrating some event I don't recall at a location I have never been before or since. It felt about the same.)
Besides: If your family volunteered to be my family this holiday it would still be your family today, next week, and next month. The best you could do would be to emulate being my family for a little while. Emulation is inherently limited. Good hearts, good food, and solicitous attention could make a wonderful holiday but they can only displace the isolation.
In actual reality it isn't being alone on the holiday that can cause distress. The isolation is real but not really unwelcome. The negative aspect of a holiday is that this one reality is excessively emphasized by the incessant contrast. Being alone is not necessarily depressing but too many people parading their group experience in front of me can become annoying.