I don’t either, but my newer TV used as a monitor requires 59.94 while my older one required 60.0. The new one is 3940x2160 (UHD) while the older one was 1920x1080 (HD)
Apparently differences in the monitors themselves. The edid data tells the system what refresh rates are available and in most cases it automatically adjusts but not always.
I had to disable VRR. I think that my DELL monitor is not supporting AMD FreeSync correctly, although it should. No matter what refresh rate I chose, full screen in games is flickering. 
Maybe I’ll wait for an official Gnome release with VRR included, and hopefully there will be fixes or enhancements so that flickering is gone. Till then, I’ll use VSync instead.
Thanks for your help here! 
Is there still no toggle button in your installation? I think I know why …
Yesterday I got my new monitor and wanted to install VRR-Package again. After installation, I also didn’t have the toggle button. So I checked all packages included in the VRR-Package. Package “gnome-control-center” in version 45.1.vrr.5-1 was not installed because there was a newer version installed from Fedora repository. So I had to downgrade the package from kylegospo repository. And now there is the toggle button in my setting. Maybe you could try this, too?