In a post on their developer blog, Microsoft has announced that with the latest Windows 10 build (1903) it has included native software controls for enabling Variable Refresh Rate (VRR) technologies.
Enables VRR for DX11 titles Without Native Support
The new feature, Microsoft says, will not replace features such as G-Sync or VESA Adaptive-Sync (FreeSync), but instead will augment them. You should still continue to use G-Sync or FreeSync normally, and the toggle will not override any existing settings for those technologies.
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.
Daniel Schlegel, Program Manager, Microsoft
In order to access the new feature, you’ll need a system with all of the following:
Windows Version 1903 or later
A G-SYNC or Adaptive-Sync capable monitor
A GPU with WDDM 2.6 or above drivers, that supports G-SYNC / Adaptive-Sync and this new OS feature