Drop your in-game resolution to 1080p or 900p. Retinal Mac displays feature incredibly high native resolutions that will crush your frame rates if not lowered.
Forza Horizon 3 was built as a Universal Windows Platform (UWP) app. Wine and CrossOver traditionally struggle with UWP apps compared to standard Win32 executables (like those found on Steam). Forza Horizon 3 Free BETTER Download Mac
To keep your Mac secure while looking for classic games, always follow these rules: Drop your in-game resolution to 1080p or 900p