To fix the "Steam must be running" error in DmC: Devil May Cry, try these verified steps from community discussions: Core Troubleshooting
Verify Game Files (corrupt config files can trigger the error) To fix the "Steam must be running" error
Pro-tip: If the error persists, ensure no anti-virus or firewall is blocking the game's connection to Steam services. To fix the "Steam must be running" error
Corruption in the game's extracted files is a common cause for this error. Open your Steam Library. Right-click DmC: Devil May Cry and select Properties. Go to the Installed Files (or Local Files) tab. To fix the "Steam must be running" error
Disclaimer: This guide is for troubleshooting technical errors. Always ensure you are running legitimate copies of software to comply with Terms of Service.