Sonic Generations is an older title. Ensure your PC has the DirectX End-User Runtimes installed.
Are you running into a specific or a black screen when you try to launch? sonic generations mods not working link
Sometimes Windows prevents HMM from writing the necessary .dll files into your Steam folder. Right-click HedgeModManager.exe and select before clicking "Save and Play." 3. Dealing with Crashes (CTD) Sonic Generations is an older title
Always ensure you are using the most recent build from GitHub. sonic generations mods not working link
If HMM is set up but the mods still won't trigger, check these three culprits: Check the Mod Order
Troubleshooting Sonic Generations Mods: What to Do When They Won’t Load
Note: You will need to re-install the Loader in HedgeModManager after doing this.