I would argue (to Iowa, this person etc) that a religion doesn’t require belief in supernatural entities to be considered valid - it could just be a philosophy, which would include TST. Some forms of Buddhism would qualify as that, too, being non-theistic - some Buddhists believe in ghosts, devas, and brahmas, but some, particularly in the west, do not. On the other hand I’m sure some Catholics wouldn’t accept that as a valid religion either. I doubt whether it has a solid legal basis though.