There are many arguments against Santa being real, so I came up with a few ideas that work out a couple of kinks without being too unrealistic.
So here’s my first theory: What if there wasn’t only one Santa? The rest of the population grows with time, so Santa’s would to. Santa has had children, his children have had children, those children have had children, and so on. At this point in time, each city has many Santas who are in charge of their own small group of people, and the rest of the Santas are scattered throughout the world. Each Santa is precisely located so that they can get as many people as possible with the given time. They would still need magic so that they wouldn’t get caught, but they wouldn’t need the millions of tons of presents for billions of children or to go at the inane speeds that one Santa would need to go to give all of those gifts. He wouldn’t even have to be immortal, because his children would be able to continue his work.
Another benefit of having lots and lots of Santas is that all those movies that show Christmas being saved by one person or the other could all be true. Every year some of the Santas would get caught by police, fall off the roof, get shot out of the sky, etc., and some group of kids, animals, and/or adults manage to save Christmas despite Santa being incapacitated in some way. Who knew all those movies were true the whole time?