Diagnosis
This is likely a conflict between the game's frame rate, the monitor's Adaptive-Sync range (48-75Hz), and the graphics card's settings.
How to Fix It
First, confirm Adaptive-Sync is on. Use the monitor's joystick: go to Game Adjust > Adaptive-Sync and set to On. In AMD Radeon Software, ensure FreeSync is enabled for the display. In NVIDIA Control Panel under Display > Set up G-SYNC, check "Enable G-SYNC, G-SYNC Compatible" for this monitor.
If That Didn't Work
The tear line indicates frames are exceeding the 75Hz max refresh rate. Cap your in-game frame rate to 73 FPS using the game's settings or the graphics driver's frame rate limiter. Do not rely on V-Sync alone.
Heads Up
This monitor's Adaptive-Sync range is narrow. If your game's frame rate drops below 48 FPS, Adaptive-Sync disengages, causing stutter. Use in-game graphics settings to maintain a minimum FPS above 50.