There are multiple ways to win in Civilzation VI: Domination, Science, Culture, Religious, or Score Victory.
-Domination Victory can be achieved by having control of all original capitals in the game. However, only the last player holding onto their capital will win, meaning if you have one last capital to go and their army takes your own capital, they would win the game.
-Science Victory can be achieved by three steps: Launching a satellite, landing a human on the Moon, and establishing a colony on Mars. Launching a satellite requires researching the Rocketry Tech, building a Spaceport, and completing the Earth Satellite project. Landing a human on the Moon requires researching the Satellites technology and completing the Moon Landing project. Establishing a colony on Mars requires researching the Robotics, Nuclear Fission, and Nanotechnology techs and completing each respective module project. Once all three module projects are built, you will have won the game.
-Culture Victory can be achieved by having a total number of tourists that exceeds the domestic tourists of every other civilization in the game. You can acheive these tourists by having multiple trade routes, shared/conflicting late game Governments, open borders, Great Works, Relics, Holy Sites, National Parks, Artifacts, and wonders.
-Religious Victory can be achieved by converting every single other civilization to your Religion, which can simply be acheived by having the majority of their cities following your Religion. This can usually be acheived by having a high number of Apostles and Missionaries.
-Score Victory is a special victory that can be obtained after the year 2050 or whichever turn the player sets. It is determined by a civilzation’s score, a score that accumulates over the course of the game from your number of civis, number of population, number of cities, number of technologies, number of future technologies, number of wonders, military accomplishments, number of Great People, and number of Beliefs.