There a couple from the Regolith project.
The older is Remontoire, a keybinding viewer.
The newer is Ilia, a Rofi-like tool which can also view and sometimes run keybindings.
But Sway doesn’t make it easy. Sway doesn’t offer an API to see the keybindings so these apps parse a special comment format.
It’s best to think of them as a cheat sheet as it won’t always work to actually to execute the actions.