Try the same mode just per application instead and see if it helps.
1. Open Nvidia controlpanel (right click on desktop).
2. Click Manage 3D Settings.
3. Click the Program Settings tab.
4. Choose Rust or PUBG from the list. If they're not in the list, uncheck the box "Show only programs found on this computer".
5. Choose Nvidia processor from the dropdown menu and select High-performance NVIDIA processor from the list.
6. Click Apply.
And is the Nvidia processor being used while playing? Download MSI Afterburner and check the performance graph during gameplay, you can post some results here if you want. I don't understand why disconnecting a secondary monitor would give you performance issues when it's most common the other way around.If you can actively connect/disconnect the monitor and immediately see performance gains/loss then either the Nvidia processors is not being used correctly or there's some kind of power-saving feature enabled somewhere. Or maybe the refresh rate is running lower than usual? I honestly don't know unfortunately
Maybe someone else here knows what's up, because I'm stumped.
Quote