Currently in Custom UI, we can use the bridge API to emit events that can be consumed by different parts of a Custom UI app: https://developer.atlassian.com/platform/forge/apis-reference/ui-api-bridge/events/

As a developer, I would like the capability to emit public events that can be capture and consumed by other apps, such as the existing events in AP for Connect: https://developer.atlassian.com/cloud/confluence/jsapi/events/