“Thanks, stranger. For the fix. And the quality.”

Fixed: Steam Says a Game Is Running When It Isn't - SoftwareKeep

The "Steam must be running" error for DmC: Devil May Cry is a war of attrition between old DRM and new operating systems. By applying these fixes—specifically the DEP exception, the antivirus whitelist, and the manual DLL recovery—you are not just fixing an error; you are systemically rebuilding the bridge between the game and the Steam client.