View: https://twitter.com/CallofDuty/status/1594800865298501632
I am going to assume that it likely counts only people who have specifically loaded into a Warzone match. Since you can have MWII installed but not have Warzone 2 installed.
Considering it took almost 2 weeks for OG Warzone to hit 30 million, going to assume this surpasses that soon.