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Following you can find the links to all Anno 1800 DLC on Steam. Please note that they're only compatible with the Steam version of the game.
Deluxe Pack: (https://store.steampowered.com/app/1066852/Anno_1800__Deluxe_Pack/)
Season 1 Pass: (https://store.steampowered.com/app/1066850/Anno_1800__Season_Pass/)
DLC Sunken Treasure: (https://store.steampowered.com/app/1125790/Anno_1800__Sunken_Treasure/)
DLC Botanica: (https://store.steampowered.com/app/1125792/Anno_1800__Botanica/)
DLC The Passage: (https://store.steampowered.com/app/1125794/Anno_1800__The_Passage/)
Cosmetic DLC Holiday Pack: (https://store.steampowered.com/app/1210040/Anno_1800__Holiday_pack/)
Season 2 Pass: (https://store.steampowered.com/app/1247710/Anno_1800__Year_2_Pass/)
DLC Seat of Power: (https://store.steampowered.com/app/1247680/Anno_1800__Seat_of_Power/)
DLC Bright Harvest: (https://store.steampowered.com/app/1314950/Anno_1800__Bright_Harvest/)
DLC Land of Lions: (https://store.steampowered.com/app/1442810/Anno_1800__Land_of_Lions/)
Cosmetic DLC Amusements Pack: (https://store.steampowered.com/app/1383240/Anno_1800__Amusements_Pack/)
Cosmetic DLC City Lights Pack: (https://store.steampowered.com/app/1465650/Anno_1800__City_Lights_Pack/)
Season 3 Pass: (https://store.steampowered.com/app/1530880/Anno_1800__Year_3_Pass/)
DLC Docklands: (https://store.steampowered.com/app/1530882/Anno_1800__Docklands/)
DLC Tourist Season: (https://store.steampowered.com/app/1626970/Anno_1800__Tourist_Season/)
DLC The High Life: (https://store.steampowered.com/app/1704680/Anno_1800__The_High_Life/)
Cosmetic DLC Vehicle Liveries Pack: (https://store.steampowered.com/app/1626972/Anno_1800__Vehicle_Liveries/)
Cosmetic DLC Pedestrian Zone Pack: (https://store.steampowered.com/app/1704690/Anno_1800__Pedestrian_Zone_Pack/)
Cosmetic DLC Vibrant Cities Pack: (https://store.steampowered.com/app/1803742/Anno_1800__Vibrant_Cities_Pack/)
Cosmetic DLC Plant a Tree: (https://store.steampowered.com/app/1803740/Anno_1800__Ornament_Cosmetic_Pack/)
Cosmetic DLC Seasonal Decorations Pack: (https://store.steampowered.com/app/1881100/Anno_1800__Seasonal_Decorations_Pack/)
Season 4 Pass: (https://store.steampowered.com/app/1933240/Anno_1800__Year_4_Season_Pass/)
DLC Seeds of Change: (https://store.steampowered.com/app/1933244/Anno_1800__Seeds_of_Change/)