This script by Mikhail Ivanyushin enables you to draw up a list of available keys when you want to create a new keyboard shortcut for some action or other in InDesign.
To work, this script needs to be placed in the InDesign scripts panel specific folder, that enables it, when run, to detect in a nearby folder the .indk file(s) containing the list of already existing hotkeys. The script then deduces from it the list of possible keyboard shortcuts that don’t exist yet and that you could use for a custom action. This list of available hotkeys is saved in a file FreeShortCuts.txt next to the script in the same folder.
The script also generate another file SameShortCuts.txt containing a list among already existing hotkeys of those that are assigned to more than one action (generally in different contexts).