I recently purchased a Y540 that has Intel i7 9750h processor and a dedicated Nvidia GTX 1660ti graphics card. From what I read online, there is something called Nvidia Optimus that controls whether something is displayed via the Nvidia graphics or Intel graphics (from the processor).

However, when I go to Device Manager and look at Display Adapters, I only see the Nvidia GTX 1660ti showing up, and not the Intel display driver. Same thing goes when I right click on the desktop, I only see one option to choose the Nvidia control panal and not one for the Intel VGA.

I tried installing the Intel VGA driver from the lenovo website for my computer but when I click setup on that driver, comand prompt breifly pops up and then goes away, and it appears that the driver does not install. I also tried installing the Intel VGA driver through the intel website for the 9750h, but when I try to install that, it tells me that my system is not compatible with that driver.

To other people that have the y540, do you see both the Intel and Nvidia display adapters in the Device manager? or do you only see the Nvidia one? How do I know that Nvidia Optimus is properly switching/using the Intel display driver when needed?

yes optimus is part of the installed nvidia driver pacakge. You can use y540 always on hybrid mode even while gaming because the optimus will use the nvidia gpu in games automatically. 

I noticed this is half-true. Nvidia GPU is indeed used on 3D games (especially when you forced it in the Nvidia Panel under 3D applications) but if you're using your laptop screen, it doesn't perform as well as when Optimus/Hybrid is off. Whereas when you play on an external screen, it performs better when Optimus/Hybrid is on. I still don't get why

You may have an HF processor like the i7-9750HF. Unfortunately they do not have an integrated graphics card.

Reinstall bios, go to bios, configuration, select switchable graphics, save, restart. Install vantage beta from microsoft store