Tech Help: Which cable to my screen for best performance

@SenorCosta  one more thing in addition to my reply above.  Since you decided to pair an NVIDIA GPU with a display that uses AMD FreeSync rather than a NVIDIA G-Sync, you might have to do some manual work to enable FreeSync support.  That's detailed here.  That article is admittedly a bit old though, so things may have changed.  If you can't get FreeSync to work at all, you might want to consider getting a G-Sync display instead, since variable refresh rate is a very handy capability to have especially when dealing with a high refresh rate display.  Then again, flight simulators admittedly aren't fast motion games like racing and first person shooters, so the benefits would be much less significant there, and possibly not enough to justify getting a G-Sync equivalent display.  Since NVIDIA owns G-Sync and charges display manufacturers for testing and certification, whereas FreeSync is open and royalty-free, a G-Sync display is usually a few hundred dollars more than the equivalent FreeSync model -- in fact some display vendors have displays that are otherwise completely identical except one variant supports G-Sync and the other only supports FreeSync.

If you can't get FreeSync working with your NVIDIA GPU and you don't want to switch displays, then you'd want to use V-Sync in your games (or enable it in NVIDIA Control Panel) but then only run your display at a refresh rate that matches a frame rate your GPU can reliably sustain.  If you try to run a 165 Hz refresh rate without FreeSync/G-Sync and your GPU can't reliably sustain 165 frames per second, then V-Sync will cause judder.  If on the other hand you turn V-Sync off, you'll get frame tearing.  FreeSync and G-Sync exist specifically to allow you to run high refresh rates without either of those problems, because they allow the display's refresh rate to adapt based on the frame rate the GPU can sustain at any given time -- but you need a GPU and display combination that allows you to enable that feature.

Use DisplayPort whenever you can.  Or if your GPU has a USB-C port, you can alternatively use a USB-C to DisplayPort cable if your other DisplayPort outputs were already occupied.  They are equivalent because USB-C carries a DisplayPort signal.  HDMI is also a digital signal and will therefore look just as sharp as DisplayPort at a given resolution.  However, at any given time the latest DisplayPort standard has supported more bandwidth than the latest HDMI standard, so some displays don't support receiving their maximum resolution and/or refresh rate over HDMI.  In those cases, HDMI obviously wouldn't be as good.  And in fact according to the Tech Specs section of the product page for that display here, that display supports up to 165 Hz over DisplayPort but "only" 144 Hz over HDMI.

In addition, some technologies are only supported over DisplayPort, such as NVIDIA G-Sync.  I'm not sure whether FreeSync works over HDMI, but it definitely works over DisplayPort.  And DisplayPort also has some other cool uses, such as daisy-chaining, although that admittedly isn't relevant to your particular use case.

@SenorCosta  I'm not sure what the "D1.4 cable" you're referring to is.  If that was meant to say DP 1.4, i.e. DisplayPort 1.4, then there's no such thing as a DP 1.4 cable that has a USB connector on one side, unless it's a USB-C connector -- but there are very few USB-C to DisplayPort cables on the market today that support DisplayPort 1.4.  If you're looking at a cable that has a "regular USB" connector that you'd plug into your PC on one end and a "house shaped" connector on the other, then that would be a USB 3.0 cable, and you would connect that between your PC and display if you wanted to be able to plug USB peripherals into the USB ports built into the display and make them usable with your PC.  But that cable would be connected in addition to a video cable.  According to the product page I linked above, that display comes with an HDMI cable, a DisplayPort cable, and a USB cable.  You'd want to use the DisplayPort cable and optionally the USB cable.

Thanks for your help and forgive my stupidity. As it turns out this monitor does have GSync capabilities. My question is that as I look at the d1.4 cable, it has just a USB on the other side. From what I understand it needs to be plugged into the video card (RTX2080) but it doesn't have something to take it. What am I missing?

@SenorCosta  if you're still having trouble identifying cables and where to connect them after reading the reply I just posted above, here is a link to the Manuals area for that display on support.dell.com.  The Quick Start Guide and User's Guide might be useful to you.