The original 2003 PC version is notoriously difficult to run on modern systems without specialized fan-made fixes [1].
Many fans prefer playing the GameCube or PlayStation 2 versions using emulators like Dolphin or PCSX2 . This often provides a smoother experience on modern hardware than the original Windows port [3]. sonic-heroes-pc-game-free-download-full-version
Since the game was released in 2003 and is now considered "abandonware" (no longer sold by Sega on digital storefronts like Steam), here is the safest way to play it today: The original 2003 PC version is notoriously difficult
Your best bet for a clean, legal version is finding a used physical disc on sites like eBay or Mercari . sonic-heroes-pc-game-free-download-full-version