Although it’s popularly believed that no new Call of Duty game would be launched in 2023, it would be incredibly unusual for Activision to really rest their prized franchise in that year. While there have been rumours about a Treyarch free-to-play game and/or a separate Zombies experience arriving in 2019, Activision has not yet made any official statements regarding either of those stories.
Activision has provided some additional clarification regarding their future goals as part of their Q2 2022 earnings report. In addition to reaffirming Warzone 2.0 and Call of Duty: Modern Warfare 2 for 2022, they also made it plain that there will be “premium” CoD content available in 2023. Activision only uses the term “premium” to describe paid PC and console games and content; free-to-play and mobile games are not included.
Another possibility is that Activision is working on a new remake or remaster, or possibly something completely unrelated that hasn’t been announced yet.