You cannot -- this is not the way the system is designed to operate.

The Intel GPU is the only one of the two that has a physical connection to the display panel.  ALL video data passes through it, even if it has been rendered by the nVidia GPU.  The nVidia GPU is effectively a co-processor.

There are some systems that allow selecting between the GPUs -- these are set up with the hardware necessary to run that way; the XPS 9570 is software-controlled -- it does not have the required hardware to run the nVidia GPU as primary.

You won't see the nVidia GPU active under Windows, which sees only the Intel GPU as a result, but if you've selected the nVidia GPU with the Optimus settings, it will be called into use for applications that need it.

Thanks a lot! That's really helpful.

But how is it decided wether an application needs the Nvidia GPU? As it currently seems everything needs it, I cant move a window around without stuttering, Youtube or VLC Video playback is super laggy and stuttering. I do have the i5 Model but still, this can't be normal. This was a quite expensive machine back when new and it's not all that old. 
I even upgraded the RAM and SSD but if there is no solution for this I need a new Notebook, which would be a huge bummer.

There are other possible causes:

First, has the system ever had a thorough internal cleaning and replacement of the thermal pads?
  If not, that would be a good idea, particularly if the system is running hot or the fans are running at high speed.

The other issue:  is the issue when local files are played, or when content is streamed?  If the latter, it could be a networking issue,not a GPU issue.

It was cleaned about a year ago, as well as the thermal paste. I even added thermal pads between the back case and components.

Both, local files and streamed content. Networking shouldn't be an issue, I got a new Intel Wireless-AC 9260 in there and get 600 Mbps on Wifi. 

I probably will clean it out again, swap the thermal pads and paste. Otherwise I'm at a loss what to do. 

Cleaned the fans, they were super clean, almost no dust.

This is what my task manager looks like when I'm playing back a 1080p video, local or streaming doesn't matter. The Intel GPU is maxed out in 3D, fans are blowing very loudly. 

Is it possible that there is a driver issue? I am out of ideas and quite dissapointed in such an expensive machine, how is it possible that my 10(!) year old Macbook performs so much better in video? playback? 

This is what I see when watching a 4k Youtube video. 

@NubianPrince​ Hey 

I recently bought an xps15 to and i have the same problem, did you already found a solution?

XPS 14 and useless RTX 4050, crazy 

This is how I managed to force my Dell XPS 15 to use the NVIDIA card instead of the Intel UHD Card.

I went to: Device Manager > Display Adapters. Right click on Intel Integrated Graphics > Disable device.

This setup will define Nvidia as default, but you can always enable Intel graphics again.

After disabling the Intel card, you'll only see one in the Task Manager

@Rishi_1976​ you can always enable Intel graphics again. why ?