Games Lagging After Installing Dota 2

Aug 8, 2018
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Recently, I installed Dota 2 on my computer. When I first started it, it asked me something about 2D rendering and DirectX 9 and stuff. I didn't bother to read and pressed ok. Now, whenever I try to play Fortnite, it lag really bad (5-6 fps average) and I have a feeling that it is linked to the messages I got. Please help me fix my issue.

PC specs:
Ryzen 5 1600
RX 570
8gb of Ram
MSI B350 Gaming plus
 
Jul 24, 2018
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Wait, you have DirectX12, right ?
And if you have Dx12 dont run your games with Dx9