Search Marquis almost always installs a rogue config profile that forces the redirect.

  1. Open System Settings
  2. Go to Privacy & Security
  3. Scroll down to Profiles (only appears if something is installed)
  4. Look for suspicious profiles such as:
    • AdminPrefs (known real Search Marquis profile)
    • Anything locking homepage/search settings
  5. Select → Remove Profile

If you see AdminPrefs, you found the primary persistence mechanism.