15 R2, Intel controls external monitor, not Nvidia

I have used 2 cables. Both support 8k resolution at 60 Hz and 4K at 120Hz and so on. My monitor resolution is 1440p (LG27 GL850 incase you wonder). The first cable has no signal, the second one has signal but as I described above. It’s weird! 

@TamFaker  Systems that allow you to change which GPU controls a given display output are fairly rare.  To my knowledge, the only Dell systems that offer it are the last few generations of the Precision 7000 Series laptops and the brand new XPS 17 9700, which include a BIOS option for this purpose -- but those systems have a more complex motherboard design to allow that flexibility.  The much more common setup is for outputs to be physically wired directly to a specific GPU.  I wrote a detailed post about the various dual GPU wiring design possibilities and their pros and cons in the first post of this thread if you're curious.  But if you decide not to read that, fyi if the USB-C/TB3 port is wired to the Intel GPU, then you won't be able to use G-Sync or Adaptive V-Sync anyway.  Those capabilities require that the NVIDIA GPU have direct control of the display output you're using.

But as for the issue, you didn't specify what display you're using or even what resolution you're trying to run at 144 Hz.  (Fyi, when asking for technical assistance, it helps to provide some general technical detail like that.)  But I wouldn't expect low display bandwidth to cause flickering.  The GPU knows the bandwidth available over the link and the amount of bandwidth the requested resolution, color depth, and refresh rate require, so it will either allow the desired setup or it won't.  It won't allow it and then flicker, unless maybe you forced that setup using a custom resolution profile.  And fyi even if you could have the NVIDIA GPU take direct control of that output, you wouldn't get more video bandwidth out of the USB-C/TB3 port anyway.  The USB-C/TB3 port and the Intel GPU in that system support DisplayPort 1.2/HBR2.  Even if the NVIDIA GPU in that system supported something newer -- which I'm not sure it does -- a system that age would only have Intel's Alpine Ridge TB3 controller, which only supported DP 1.2.  Support for DP 1.4 didn't arrive until Intel's Titan Ridge controller generation, which didn't arrive until 2019, years after your system was made.

So again, you might want to just try another USB-C to DisplayPort cable.  But if that doesn't work, then if you don't want to use HDMI either, and given that the 15 R2 doesn't offer a Mini-DisplayPort output like newer models, it seems you'd be stuck.

@Alienware Area-51 ALX 2006  No, that isn't a plausible theory.  A cable that supports 8K resolution (which is just a cable that supports DisplayPort 1.4/HBR3) doesn't become unusable if you use a display with lower resolution and/or a system that doesn't support driving that.  You can use DisplayPort and HDMI cables certified for 4K 60 Hz with devices and TVs/displays that only support 1080p, for example.  The maximum capability of a cable doesn't imply that it has a minimum capability.  And if that were the case, it would be reasonable for the cable manufacturer to call that out on its product page to avoid a lot of returns (and realistically if that were the case, they'd get returns anyway from people who didn't read the details).

I'm not sure what accounts for the behavior reported here, but I don't see how the answer could reasonably be using a cable that is certified for a higher level of performance than is necessary and/or supported by the system.

Well the reason why the first cable didn’t work because it’s made for an 8K device right?

so the Graphics card on the laptop, including the discrete one can’t provide enough bandwidth to display an image that large. Don’t try it, I’ve done that before with my Alienware 15 r1 with the 980M on a 8K tv. The TV said no signal and my GPU fans started to ramp up.

Sorry about that.