Nvidia and AMD had a heck of a time getting G-Sync and FreeSync to work on Windows, but with Intel finally adopting the feature, variable refresh rate (VRR) appears to be well on its way to becoming a standard feature for Windows PCs. That means Microsoft needs to lurch to action, and it has: a post on the DirectX Developer Blog specifically highlights the new "Variable refresh rate" setting in Windows 10 version 1903.
According to the blog post, the setting "enables VRR support for DX11 full-screen games that did not support VRR natively." That seems a little curious to this writer, given that historically it was DirectX 11 games running in exclusive full-screen mode that best-supported VRR, and they generally didn't need any game-specific support to do so. Whatever the case, if you'd like to enable the feature yourself, it's in the "Graphics Settings" panel of Windows Settings.
Unfortunately, I can't actually test the new feature because it isn't showing up for me. Microsoft says the toggle won't appear unless you have Windows version 1903 or later, a VRR-capable monitor, and a GPU with WDDM 2.6 (or above) drivers that also specifically support this new feature. I check two of those three boxes, so either GeForce driver version 430.64 doesn't support the new feature, or it's not available on my edition of Windows.
If you're worried about Microsoft's feature interfering with the already-quite-functional VRR implementations built into major graphics card drivers, you apparently needn't be. Microsoft says that this toggle "doesn't override any of the settings you've already configured." The company says this new OS support is merely intended to augment the existing technologies, not replace them. Having OS-specific support should really only improve the compatibility of VRR going forward, so it's nice to see Microsoft bringing this feature into the OS.