If you missed a free window, Anno 1800 is a staple of seasonal sales. It regularly drops to for the base game. For that price, you get one of the most beautiful city-builders ever made, featuring:
Ubisoft frequently hosts Free Weekends (often aligned with major updates or anniversaries). These give you access to the full base game for a few days, and your progress carries over if you decide to buy it later. anno-1800-free-download-pc-game-version
The Ubisoft+ subscription service often offers a 7-day free trial . Since this includes the Definitive Edition , you can play the base game plus all 12 major DLCs for free during that week. If you missed a free window, Anno 1800
The "Free" version might give you the gameplay, but the "Official" version gives you the mods and community blueprints that make the late-game manageable. These give you access to the full base