At the very end of the game, Aloy speaks to Elisabet Sobeck in a monologue where she talks about how there’s one more fight they have to win.

“My friends have a new mission,” Aloy said, “to spread the word and ask for help.” Here, we see each of Aloy’s friends going back to their respective tribes to ask them all to support her in this battle. So, if there’s going to be another fight, there’s got to be another game.

Source: https://www.distractify.com/p/horizon-forbidden-west-sequel