I questioned it around 8 and fully stopped believing around 10. When you behave and ask for the same gift three years in a row you start to wonder. Before that I believed that he was magic and was incredibly fast.
Years ago I didn't want to teach my children about Santa because of the Christian connections, but then I realized why we have holidays over winter. If it makes them happy I'll do it, but I'll also be teaching them about all the other connections to pagan religions when they're old enough to understand.
Same reason why we create all sorts of other things for kids. To allow kids to be kids and have fun. To help them see the good in the world before we rip the rug out from under them, and show them the world just plain fucking sucks.
Kids can have fun without that lie: "Let's make cookies together and eat them. Let's hang up stockings and put surprises in them for each other. Let's decorate a tree and make a fun video".
Being lied to by your protector and guardian is enough to traumatize anyone at that age. You shouldn't be shaming the people who get hurt by it, you should be shaming the people that do it.