Macbook Pro 2019 Bootcamp external display switches to 30hz when laptop lid is closed
As it turns out, this is an issue with the 2019 Macbook Pro and Bootcamp/AMD drivers. The solution is easy. Switch the resolution to something other than the default, and watch as the refresh rate magically increases to 60hz. Then just set the resolution back to the default setting and the refresh rate will still be at 60.