Did you enable this function in the monitor?
(A). For AMD GPU with FreeSync:
You need to look at page 31 of the User Manual here:
FreeSync FreeSync technology is solution that eliminates screen tearing without all the usual lag and latency. This feature will eliminate screen tearing and lag during game play. Improve your gaming experience. The displayed FreeSync menu items on the monitor may vary, depending on the monitor model and compatibility with the AMD graphics card. • Off: Disable FreeSync. • Standard Engine: Enable the basic FreeSync functions of the AMD graphics card. • Ultimate Engine: Enable the FreeSync feature with a higher screen frame rate. Screen tearing (abnormal sync between the screen and content) is reduced in this mode. Note that screen flickering may occur during game play. Apply the optimum resolution when using FreeSync. The refresh rate setting method please refer to Q & A → How can I change the frequency? ― The FreeSync function is only enabled in HDMI1, HDMI2 or DisplayPort mode. Use the HDMI/DisplayPort cable provided by the manufacturer when using FreeSync. If you use the FreeSync function while playing a game, the following symptoms may occur: • The screen may flicker depending on the type of graphics card, the game option settings, or the video being played. Try the following actions: decrease the game setting values, change the current FreeSync mode to Standard Engine, or visit the AMD website to check your graphics driver’s version and update it with the latest one. • While you are using the FreeSync function, the screen may flicker due to variation of the output frequency from the graphics card. • The response rate during the game may fluctuate depending on the resolution. A higher resolution generally decreases the response rate. • The sound quality of the monitor may be degraded. ― If you encounter any issues when using the function, contact the Samsung Service Center. ― When the resolution is changed while setting FreeSync to Standard Engine or Ultimate Engine, the screen tearing can happen intermittently. Set FreeSync to Off and change the resolution. ― The function is unavailable in the devices (e.g. AV devices) that have no AMD graphic card. If the function is applied, the screen may have malfunction. ― For optimal screen images, Brightness may be adjusted in FreeSync mode depending on the input content.
How do you enable FreeSync?
1 Set FreeSync to Standard Engine or Ultimate Engine in the OSD menu.
2 Enable FreeSync in AMD Radeon Settings:
Right-click the mouse → AMD Radeon Settings → Display The "AMD FreeSync" feature should be set to "On". Select to "On" if not already enabled.
(B). For Nvidia GPU's. According to the Nvidia CES 2019 "Keynote presentation", Nvidia GTX10 series and RTX 20 Series GPU's will support FreeSync using a new Nvidia Driver Update starting on Jan 15 2019. If you know anyone with one of those GPU's you could ask them to try it out for you. I will be testing it out on an RTX2080 which I already use with a FreeSync Monitor without any problems at 4K 60 FPS refresh rate - (with FreeSync off).
I currently use Nvidia Adaptive Sync with VSync on anyhow and it produces good results with no stutter (Adaptive Sync) or screen tearing (VSync is on).
The RTX2080 is powerful enough to maintain 4K 60FPs in many cases.