As you can probably infer from the title, this error is directly related to DirectX 12 being supported by your PC, as GPU might not be able to handle it. However ...

Check that you have DirectX 12 installed on your PC Reinstall DirectX 12 if files are corrupted Update your GPU drivers Add launch options parameters to TFD on Steam ...

League of Legends players often encounter error codes that force-shut the client and do not let a player log into a match ...