By default, these type channels are not linkable to Items - they make events, not states.
Because they are transient events, the usual way to use them is to trigger a rule from the event, and no Item is involved.
You quite likely might not need to be on this path at all - “This is not the feature you are looking for” perhaps?
Having said that -
There is a set of rarely-used “raw” system profiles, that modify trigger channel output and allows linking to an Item. You don’t need to import them
A few bindings will also bundle in their custom profiles.
I wouldn’t be surprised if the GUI does not offer trigger profiles correctly. You should be offered at least the timestamping profile for any trigger type.
I do indeed want to trigger a rule from the event, for example:
I guess that is not possible with events?
Previously, in order to be able to display custom strings from a homie item in openHAB BasicUI, I have had to make the item retained. In fact, my Homie library has a “Fake Retained” flag, which flags the Homie parameter as retained, even though it isn’t actually retained. This way openHAB 2.x treated it as a string so that I could link an item to it. I didn’t have time to dive into the issue at the time and just needed it to work.
Does that mean I should still use that same workaround?
I don’t know if there is something unique to how Homie works in this regard but typically an Event Channel can be used to trigger a rule and if there is any data that comes with the event, that data will be in event.event (if using a non-Rules DSL language) or receivedEvent using Rules DSL.
In non-Rules DSL languages, there is also event.channel which will have the Channel ID of the event Channel that triggered the rule.