For Irish citizens:
You do not need an ETA or ETAS for the UK or the Schengen area.
Your Irish passport is valid in the EU from the first day of issue to the last day of issue.
You do not need any authorisation for the UK or EU to travel.
You have the same rights as a UK citizen to live and work in the UK and vice versa for UK citizens in Ireland.
You have the full right to work in any EU country from the moment you set foot in that country.