The SCHEMA:PATH part seems slightly wrong (singular vs. plural). Try:

schema=org.gnome.settings-daemon.plugins.media-keys.custom-keybinding
path=/org/gnome/settings-daemon/plugins/media-keys/custom-keybindings/custom1/

gsettings get "${schema}:${path}" binding
gsettings get "${schema}:${path}" command
gsettings get "${schema}:${path}" name

I’d write a bookmarklet for that case:

javascript:
{
const name = 'ABC';
const d = new Date();
const year = d.getFullYear();
const month = d.getMonth();
const date = d.getDate();
document.activeElement.value = `${year}/${month}/${date} ${name}`;
void 0;
}

This bookmarklet inserts the desired text into the currently focused text box. Tested on Lemmy Web UI.

What program are you using to write or edit the comments?

As already suggested, take a look at i3 Window Manager’s docs: https://i3wm.org/docs/userguide.html because Sway (works on Wayland) is a port of i3 (works on X11).