If you're using a 60% keyboard, or any other layout with no F-row, you will have noticed that there is no dedicated Escape key. Grave Escape is a feature that allows you to share the grave key (<code>`</code> and `~`) with Escape.
Replace the `KC_GRAVE` key in your keymap (usually to the left of the `1` key) with `KC_GESC`. When pressed it will behave like `KC_ESC`, but with Shift or GUI held it will send `KC_GRAVE`.
There are several possible key combinations this will break, among them Control+Shift+Escape on Windows and Command+Option+Escape on macOS. To work around this, you can `#define` these options in your `config.h`: