15 R3, no G-Sync after changing motherboard

That's a bummer, Thank you tho

I agree with ejn63's post.  G-Sync requires the NVIDIA GPU to have direct control of the display outputs.  On most systems, the outputs are wired to the Intel GPU and then the NVIDIA GPU operates only when needed and then purely as a render-only device that passes completed video frames through the Intel GPU.  The benefit to this design is that the NVIDIA GPU can be completely disabled when its performance isn't needed, which helps battery life.  The drawback is that you can't use certain technologies that the Intel GPU doesn't support passing through and/or that require direct control from an NVIDIA GPU.  These include G-Sync, Adaptive-V-Sync, VR, and stereoscopic 3D.  And sometimes other differences relating to max display resolution and bandwidth can come into play.  For example, some systems have an Intel GPU that only supports 3 total displays, 4K resolution, and DP 1.2/HBR2, and an NVIDIA GPU that can support 4 total displays, 5K-8K resolution, and DP 1.4/HBR3 when it controls the outputs.  If the system has the outputs wired to the Intel GPU, then you're subject to that GPU's limitations in that regard.

@Elsrougy  I'm not sure what's going on there.  It's possible that you've now created a pairing between a motherboard that doesn't support G-Sync and a keyboard that has a toggle button that's meant for G-Sync systems and shouldn't exist on systems that don't support it.  In that case, you might be able to send some sort of command to that motherboard that simply isn't valid for its design.  Normally in this case I'd expect the motherboard to disregard a command that would lead to an unusable result as in the case here, but sometimes weird things happen in edge cases like motherboard swaps.  But I also don't have specific expertise about this system, so I can't say for certain what's going on.  Typically on systems that allow the GPU controlling the outputs to be changed, the change is made through a BIOS option.  But based on the behavior you describe and especially the requirement for a restart, it sounds like there might be a shortcut key to toggle this feature along with some software in Windows to facilitate the switchover.

Okay so here's an update:

there is a button on the laptop for (discrete graphics always enable) but when I do that the monitor goes black and I had to use an external monitor in order to return it again to use integerated graphics (there is a prompt on the screen that I have to click with the mouse to restart), doesn't that mean that it can route directly to the discrete card or smth like that but it's not working for some reason?

@jphughan that makes sense, there is no option in the bios for switching GPUs and I guess what happens when I click that button is that it send the command to the motherboard and the motherboard excutes it without supporting the command that's why it's not working.