To install the NVIDIA driver that System76 provides use this command:
sudo apt install system76-driver-nvidia
Open NVIDIA X Settings, go to ‘X Server Display Configuration’, then select ‘Advanced…’ now click “Enable SLI Mosaic”.
Select each of the orange colored displays and change their ‘Configuration’ to ‘X screen 0’.
Select ‘Save to X Configuration File’ and now click ‘Save’. Once the computer is rebooted the new settings will take effect.