I have recently been venturing into older CODs to replay the Zombies maps since the mechanics of the older games are a lot more fun than the newer ones. To my surprise, they have solid playerbases even today. Can’t say for sure that the PvP multiplayer modes have players anymore, but jump into World At War if you want a WWII game!
Also, confidently accept that there will never be another Call of Duty built with an ounce of passion. That age is long gone.