The implementation of the "disabled" property uses the event handler in paper-button:   https://cs.chromium.org/chromium/src/chrome/browser/resources/chromeos/login/oobe_buttons.js?q=oobe_buttons.js&dr&l=31

onClick_ should receive the event first, and if the "oobe-text-button" has "disabled" property, the event should stop bubbling up, therefore any event handlers in "oobe-text-button" should be no-op, and the button is effectively disabled.

However, right now click events can never reach the "paper-button" level: we found that the event only reaches the outer level of "oobe-text-button", but does not go down.

This looks very similar to the "closed-shadow" section in https://developer.mozilla.org/en-US/docs/Web/API/Event/composed. However, this should be a regression since it used to work.