Many Feesync monitors come with Freesync disabled. Often they don't call it FreeSync in their menus either. May be something like adaptive sync or in your monitor specs going by the specs I posted below the setting may be call no-sync. Make sure it is enabled. Also know that the native speed for your monitor is 144 and that 155 is an overclock available on Display Port only. If you don't have a quality display port cable that can limit things too. If your monitor came with it, the one you have should be fine.
Next once that is done you will want to set your FreeSync range with chill you set the limit to be one inside of the max and min for you monitor. Your native range is 40 to 144 so the Chill Range would be 41-143 or 155 if you feel the need to Overclock. My bet is you would be better to just leave it at 144 as that is common speed that most game settings would respect.
Your monitor also has a driver and it would need to be loaded if you have not (sounds like you had but make sure it is the Dell driver is installed and not the Windows Generic PNP). Also fyi Windows after some updates is known to change the driver back to the generic PNP, so if you have future issues make sure to install the monitor driver again.
The driver download is here:
Support for Dell S2719DGF | Drivers & Downloads | Dell Albania
Specs:
Display
- Diagonal Viewing Size:
68.47 cm
27.0 Inches
Preset Display Area (H x V):
596.74 mm x 335.66 mm
23.45" x 13.19"
201076 mm² (311.67 inches²)
Panel Type:
Twisted Nematic (TN)
Display Screen Coating:
Antiglare with 3H hardness
Maximum Preset Resolution:
2560 x 1440 at 155Hz (Overclock with DP)
2560 x 1440 at 144Hz (Native with HDMI 2/ DP)
2560 x 1440 at 60Hz (Native with HDMI1)
Viewing Angle:
(160° vertical / 170° horizontal)
Pixel Pitch:
0.2331 mm
Pixel Per Inch (PPI):
109
Contrast Ratio:
1000: 1 (Typical)
8 Million: 1 (Dynamic)
Aspect Ratio:
(16:9)
Backlight Technology:
LED edgelight system
Brightness:
350 cd/m² (typical)
Response Time(typical):
1ms (gray to gray)
AMD Free-Sync™:
Yes (with option for No-Sync)
(Supports Free-Sync 40Hz-144Hz (HDMI) and can be overclocked to 155Hz via DisplayPort only)
AlienFX™ Lighting:
No
Adjustability:
Height adjustable (130 mm)
Tilt (-5° to 21°)
Swivel (-45° to 45°)
Pivot (-90° to 90°)
Built in cable-management
Dell Display Manager Compatibility:
Yes
Low Blue Light:
Yes, ComfortView
Flicker-free:
Yes
Color Support:
Color Gamut (typical): 84% (CIE 1976), 72% (CIE 1931)
Color Depth: 16.7 Million colors
Flat Panel Mount Interface:
VESA (100 mm)
Audio Output:
No
