Chinese vs. American Mahjong
Although they share the same roots, Chinese Mahjong and American Mah Jongg are very different games. They use similar tiles, but the rules, objectives, strategy and even the spelling of the name differs.
Chinese Mahjong

Crazy Rich Asians
Chinese Mahjong emphasizes flexible hand-building and traditional pattern recognition.
Created in China around 1850
144 tiles consisting of Suits (Circles, Bamboo, Charactors), Dragons, Winds, Flowers
Winning mahjong hand is: 4 melds consisting of Chows (run of 3 tiles), Pungs (3 of the same tile), Kongs (4 of the same tile) + 1 pair
No card - hands never change
Basic game is similar to rummy card games
Score is based on the combinations of tiles - all players calculate their score
Usually played without racks and larger tiles
Chinese Mahjong is the original game played worldwide with slight regional variations.
American Mah Jongg

The Marvelous Mrs. Maisel
American Mah Jongg emphasizes planning around a published set of hands, making effective use of jokers, and strategic tile passing at the start of the game.
Created in the US around 1920
152 tiles (same as Chinese + Jokers)
Winning mahjong hands are dictated by a card from the National Mah Jongg League that changes every year in April
Score is also dictated by the annual card - usually winner-take-all
Features a tile-passing phase (called Charleston) at the beginning of the game to swap unwanted tiles with other players
Played with racks and smaller tiles
American Mah Jongg is not simply "Mahjong played by Americans." It's a specific ruleset developed from Chinese Mahjong but became substantially different.