Activision has yet to reveal any details about the next Call of Duty entry after Vanguard. However, leakers supposedly got their hands on some screenshots of the early build of this next title. Potentially, the next entry could be set in the future and could be another Black Ops entry.
According to Nice_Reputation_4784's thread on the GamingLeaksAndRumours subreddit, some leakers secured the screenshots of the in-development build of this next Call of Duty entry. As seen on the screenshots, the guns in this entry will be futuristic once again and is said to be the "Black Ops T10" build. In development, Call of Duty Vanguard had the T9 codename when it was still in production.
Call of Duty 2023: Leaked Images Show Futuristic Black Ops Entry Again
If this leak proves true, the developers could be revisiting the later Black Ops entries which tackled soldiers armed with equipment in the near future. The series also featured characters connected to Alex Mason and Frank Woods. If it's also a Black Ops entry, Treyarch could be up to the task once more.
For now, Activision is still supporting the Call of Duty Vanguard having only released in November 2021.