Mathematical Platonism

Jimrandomh has addressed this well. I'll add that if you feel as confident of reductionism as the last two items on your list would suggest, it seems odd to reject out of hand the idea that we could reduce everything to math. (I don't believe in any version of Tegmark IV, but I'm open to arguments.)

For all I know, many who claim to believe in Platonism have something like this in mind, and it just isn't clear to you because philosophical terminology is not optimized for your understanding (or, indeed, for any individual's goals).