My Razer 15 won't use the GPU onboard?

So the reason why you cannot connect directly to your discrete graphics card is because your laptop probably does not have a Mux Switch on it. In most cases with gaming laptops, what will happen is your Laptop will have it's screen connected to your integrated graphics (in this case, the Intel UHD Graphics) but then it will have your discrete GPU run in the background. This is to help save battery on the laptop as gaming laptops typically are so limited on power, considering that they will consume more power than a regular laptop. However, if you have a Mux switch on your laptop, then that will allow you to completely bypass the Integrated Graphics, and go straight to your discrete graphics, although you do need to have your Advance Optimus turned on. I had this same problem on one of my gaming laptops. I am an Alienware user, so I don't use Razer (though I have thought about getting a Razer Blade in the past), but I can assure you the same thing applies here. On my first Alienware laptop, the m15 r3 with a 60hz 4k screen, I had the same problem where I could not connect to my 2070 super that was built in because I did not have a Mux switch. Now I've upgraded to the m15 r6 with a 3070 GPU and a Mux Switch, and now I am able to use my 3070 with my built in laptop screen. If you don't have a Mux switch on your laptop, you will probably need to buy a new one as they have to be built into the system, although if you plug an external gaming monitor into your current laptop without the mux switch, then that will allow to you bypass your integrated graphics and go directly to your discrete graphics card. Hope this clears some things up.