But by the time Jaime reaches the city, Cersei has already killed Missandei (), leading Daenerys to launch her attack, with the dragon Drogon raining fire upon the city.

Source: https://collider.com/game-of-thrones-jaime-brienne-romance/

Daenerys, alone with Drogon, encounters a rival Dothraki clan, while her friends in Mireen are surrounded by enemies.

Source: https://collider.com/the-winds-of-winter-george-r-r-martin-game-of-thrones/

Feeling guilty that it was his actions that left Drogon with no one to tame him, this might spur him to return from Beyond the Wall and go in search of Drogon.

Source: https://screenrant.com/game-thrones-drogon-after-daenerys-death-body-where/

Feeling guilty that it was his actions that left Drogon with no one to tame him, this might spur him to return from Beyond the Wall and go in search of Drogon.

Source: https://screenrant.com/game-thrones-drogon-after-daenerys-death-body-where/

The most likely of these, which has been speculated since the finale, is that Drogon went back to Valyria.

Source: https://screenrant.com/game-thrones-drogon-after-daenerys-death-body-where/