I was trying to play Minecraft using my NVidia GTX 1060 using the "Advanced graphics settings" menu/options (Windows 10 1803+ only), adding a new entries (java.exe, javaw.exe and MinecraftLauncher.exe) and choosing the NVidia card, because my display is connected to the Intel UHD 630 HDMI port.
 
What I expected to happen was...:
When I press "Play", it should have opened Minecraft. Same all other games.
 
What actually happened was...:
Instead, minecraft ignored that policy and gets opened using the Intel UHD 630.

Also, in old versions like 1.12.2, Im getting this nice crash:

The game crashed whilst initializing game
Error: net.minecraft.client.renderer.StitcherException: Unable to fit: minecraft:blocks/lava_flow, size: 32x32, atlas: 0x0, atlasMax: -1x-1 - Maybe try a lower resolution resourcepack?
 
Steps to Reproduce:
1. Disconnect all monitors from the dGPU card.
2. Plug your display to the Intel iGPU, go to "Display settings" > "Advanced graphics settings" and add java.exe, javaw.exe and MinecraftLauncher.exe to the "Classic applications" list, and choose the dGPU card.
3. Open the MinecraftLauncher (Launcher will get loaded into dGPU, check it with GPU-Z) and press the "Play" button. Minecraft doesnt care about that policy. Also, you will get a crash using 1.12.2 or earlier versions.