Hey, I found a fix so you can still have your Sli on and still play KI.
A youtube video showed to change the game settings in Nvidia control panel -> Manage 3D settings(on the left) . Click the tab “Program Settings” -> Select Killer instinct and turn on Antialiasing FXAA.
This worked for me hope it works for you guys as well .I was stumped too, then I saw this video online below which showed the steps so I am sharing this video as well in the link below. Be sure to thank him if it works.