No G-sync in Nvidia Control panel

@Thequila  there are possibly two problems in your scenario.

The first problem is that I'm not sure about FreeSync, but I know that G-Sync only works over DisplayPort, including a USB-C connector that supports DisplayPort video output.  It does not work over HDMI, so that might be why FreeSync isn't possible.  And even if FreeSync itself supports HDMI, that doesn't necessarily mean that NVIDIA GPUs support FreeSync over HDMI.

The second possible issue is that the Inspiron 7657 might have its display outputs all wired to the Intel GPU.  In systems set up like this, the NVIDIA GPU is activated as a "render-only" device when needed, doing all of the render work and then passing completed video frames to the Intel GPU for passthrough output to the attached display(s).  This technology is called NVIDIA Optimus, and the main reason it's implemented is to improve battery life, because this setup means that the NVIDIA GPU can be completely powered off when it isn't needed, whereas if it had direct control of video outputs, it would need to remain active whenever a display was connected, even if nothing graphics-intensive was going on -- and some people use external displays even while running on battery power, such as when giving presentations.  Unfortunately, G-Sync (and possibly FreeSync) does not work through NVIDIA Optimus; it requires the NVIDIA GPU to have direct control of the display output, because the Intel GPU doesn't support passing G-Sync through, so this might be an issue with FreeSync as well.

If you want to see which GPU controls your display outputs, go to the PhysX Configuration section of NVIDIA Control Panel.  That should show you which GPU has direct control of each output where a display is active.