naja078 This is correct, sadly. The EA App only supports macOS Catalina (10.15) and newer, and Catalina and newer versions of macOS can't run 32-bit apps, including Sims Medieval. So there's no reason for the EA App to support Medieval—no version of macOS can run both the App and the game.
Since EA rereleased Sims 1 and 2, and created a 64-bit version of Sims 3 for macOS, there's always a possibility that it will adapt Medieval to run in newer OSs as well. But until then, your only option is to play the game in Windows.
Speaking of which, if you can run El Capitan on your Mac, you can use Boot Camp Assistant to partition the drive and install Windows 10. That would run Medieval and any other 32-bit game available for Windows.