Vsync & FPS

Vertical Sync (in Editor) - The graphics technology responsible for synchronizing the frame rate of a game to the refresh rate of a monitor.

Max FPS - Frame rate is the frequency at which consecutive images are captured or displayed. This feature is particularly useful as you can stop your GPU from running as fast as it can. This will save battery power and reduce heat consumption, letting you game for longer when you're away from a power outlet.

https://docs.unrealengine.com/4.27/en-US/TestingAndOptimization/PerformanceAndProfiling/SmoothFrameRate/