Go to OBS settings.
Go to Output tab.
Switch output mode to Simple.
Go down to Recording and change Quality to Indistinguishable.
Change Format to MKV.
Change Encoder to Software (x264 low CPU usage preset)
If that encoder causes too much action, and things aren't smooth enough, you can alternatively try the Hardware (QSV) option.
And if that isn't smooth enough, then last ditch effort is to try using the AMD option, but save that as a last resort because it's not very good.
Ignore everything else that I DID NOT mention, and ignore the blue highlighted NVENC option because I have my own encoder settings set up using advanced options for my hardware, I just switched things over real quick to be able to take a screenshot of what I was...