I have a 60Hz monitor overclocked to 75Hz via Nvidia control panel and it works and the monitor recognizes the custom refresh rate when on the desktop but when in game, the monitor says it's getting a 60Hz signal and turning Vsync on locks the game to 60fps. Not entirely sure in what version this broke, but the custom refresh rate works in 1.12.2

How to reproduce:

1. Create a custom resolution in Nvidia control panel set to 75Hz
2. Open the game. The HDMI signal gets set back to 60Hz and VSync locks to 60FPS