The long-awaited Call of Duty game for 2021, rumored to be titled Call of Duty: Vanguard, is apparently going to be revealed very soon.
Activision used to announce their next next Call of Duty game by May of every year and did this until Call of Duty: Black Ops Cold War. Cold War was instead announced in the summer of 2020, followed by an official release just a few months later. The deviation was probably due to the COVID-19 pandemic.
Although the name of the game has been rumored to be "Vanguard" for the longest time, the placeholder name of Call of Duty 2021 was accidentally updated on Battle.net with a new name - "Call of Duty: Slipstream", along with a new logo. As you can see below the logo certainly has a World War II vibe, which is when the new game is set.
Call of Duty: Vanguard is expected to be revealed some time during August 2021, via some sort of special announcement or in-game event in Call of Duty: Warzone.
Warzone and Black Ops Cold War are fast approaching the end of Season 4 and are season 5 is scheduled to begin on August 12, 2021. So the Vanguard reveal event could take place at either the start of season 5, or later in the season.