I don't much like Christmas on my own, but you get used to it. Tree up on 20th, small turkey breast and all the trimmings for Christmas Day and Boxing Day, and freeze the leftovers. Two presents under the tree, one for and one from my cat. Stick a "happy face" on and go for a walk in the morning, and see who I can chat to. It's soon over but I feel better having made the effort.
Worse than Christmas Day is the run up. When I was a child, the build up to Christmas started on the first of December, now it starts earlier each year, last year, even with Covid, the adverts, decorations etc started in September. If anything makes me feel sad, it is the four months of constant reminders that I will be alone for the big day.