I got it working fine now. I hope it works for you, but if you’re on Windows 10 go to your Settings, go to Display, at the bottom open Graphics settings, then click browse and open Steam>steamapps>common>Warhammer 40,000 DARKTIDE>binaries and then select Darktide and add it to the list. Click on it and select Options and then select High Performance. Worked immediately for me I hope it does for you too! 
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