With Windows Version 1903, Microsoft has added a new toggle in Graphics Settings for variable refresh rate. Variable refresh rate (VRR) is similar to NVIDIA’s G-SYNC and VESA DisplayPort Adaptive-Sync.
This new OS support is only to augment these experiences and does not replace them. You should continue to use G-SYNC / Adaptive-Sync normally. This toggle doesn’t override any of the settings you’ve already configured in the G-SYNC or Adaptive-Sync control panels. This new toggle enables VRR support for DX11 full-screen games that did not support VRR natively, so these games can now benefit from your VRR hardware.
For more, check out this Microsoft blog.