Didnt they have some sort of production issue that caused them to start late?
I expect Series X+S, to be lower first year than Xbox One was.
For reference, here is what the Xbox One sold through in its first full calendar year, according to VGC estimates:
Yep pretty sure, Series X+S does less than this in its first calendar year.
After giveing it a little more throught, I think it ll probably be abit over 6m.