How to change refresh rate on an external display on macOS. Useful if for some reason macOS decides to no longer drive your 4k display at 60Hz and gives you no option to correct.

fix-refresh-rate.sh

# install cscreen
brew cask install cscreen

# list displays
cscreen -l

# find your external screen in the list and write the number (not the ID) down somewhere
# in the following instructions, use that number instead of <SCREEN>

# list display modes for your external screen
cscreen -s <SCREEN> -v

# find a display mode you like and run
cscreen -s <SCREEN> -x <HEIGHT> -y <WIDTH> -r <REFRESH_RATE>

# if that doesn't work (which it sometimes doesn't, even though the resolution/setting is listed in cscreen -v) 
# try channging to a different resolution, then back to your desired resolution
cscreen -s 2 -d 32 -x 3840 -y 2160 -r 60 
cscreen -s 2 -d 32 -x 2560 -y 1440 -r 60