We have known the format for Champs since March

its right here lol this was posted way back in March before Reykjavik. idk why a lot of people seemed surprised. (It's in the big poster image with the whole VCT overview for the year)
https://playvalorant.com/en-us/news/esports/2021-valorant-champions-tour-overview/

Noone :

Riot : Releases smth and updates smth

The Community : U SUCKKKK , INDIE COMPANY , RITOOOO C ANT UPDATEEE , CSGOOOOO > VALORANNTNTNT BATCHEST

they also made a whole video for the format before Reykjavik

oh it might not be a direct 16 team double elim then, even for masters it says a 16 team double elim bracket even though there were groups so this might have groups as well