I think your games are using the default Intel GPU instead of the Nvidia GPU (hence poor game performance) because you haven't used Nvidia Control Panel to assign the Nvidia GPU to each installed game.

Use Nvidia Control Panel to choose the preferred GPU for each game - you only have to do it once.
 
Jun 2, 2018
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On the control panel, I made sure that Nvidia is set as my preferred GPU and all the global settings are for Nvidia