Purchase the Windows version of Anno 1503 from GOG.com.

Anno 1503 is a masterpiece trapped in a time capsule. Apple’s aggressive move to 64-bit and ARM architecture killed native backward compatibility. You cannot simply download a double-clickable app.

Since there is no official Mac version, you will need a compatibility layer to run the Windows version of the game. Porting Kit (Recommended) Porting Kit

The free download is not a file—it is a methodology. You must be willing to use UTM (virtualization) or learn Wine configuration.

Below is everything you need to know about getting running on your Mac. Is There a Free Mac Version?