The correct way is to edit the platform.props file:

change

<WindowsTargetPlatformVersion>8.1</WindowsTargetPlatformVersion>

to

<WindowsTargetPlatformVersion>10.0</WindowsTargetPlatformVersion>

After restarting Visual Studio, you can see the change in the UI.

https://developercommunity.visualstudio.com/t/unable-to-change-the-windows-sdk-version-for-proje/169374