There isn’t a easy menu in macOS to prioritise applications for high performance over others. I couldn’t get the Atmonitor software to work ,so I did some more digging and came across the renice command. I successfully improved the stream quality on OBS by prioritising the program.

Renice Command Explained
sudo renice -20 3524

To run the renice command you need to specify the priority number and the target application/process ID. In the example you can see the ID number for OBS streaming software, It’s under the PID column.

sudo renice (amount from high -20 to 20 low, Yes -20 the highest performance) (PID number from Activity Monitor)
Open up Mac Terminal and write the command.
Note: ALL Applications are defaulted to renice 0!
Then hit Enter, and put in your administrator password (if needed).
That’s all, you should have now reprioritised your choose application. This is only a temporary change to your mac and all settings will go back when you restart.