There are several popular games at the moment. Depends on what you want to play. Call of Duty has a new game out if you like WW2 first person shooters. Forza Horizon 5 is also popular at the moment, thats a racing game if you like those etc.
It's very hard to define the most popular game in overall. What are the criteria? Numbers of sold copies? Current number of players? It's easy to identify the most popular online game. It's still World of Warcraft. The popularity of this game has fallen down a little during the last few years, but it still draws more players than any other game from this genre.