How to Enable Server App to use Multithreaded Cores? Maxes 1, then lags without using other cores

[animusesports]

Essentially, I'm watching the server max out 1 core on this multithreaded core, then just lag after sustaining a certain amount of connections. I see the USEALLAVAILABLECORES as an option client side, but what would help for serverside?

Thanks a lot, everyone!