cash in Ireland in 2023

You don't need any unless your lodging or a boat trip is cash only. There are a few B&Bs that don't use Booking,com and the like and they often expect (and warn you) that they expect cash. I have Google Pay on my cellphone, and don't even need a credit card or wallet.

My experience in rural Ireland earlier this month was that we needed cash to get on a bus in Dingle (no bus station). We also needed it for laundry. We used some for tips. If you're not taking rural buses or doing laundry, you're probably okay.

We always carry some local currency no matter the country.
I seem to remember needing a coin for a public bathroom at the Heuston train station but that was a.while ago. To us it is better safe than sorry.

We spent 3 weeks in Ireland this past July. On arrival I withdrew 100 euros from an ATM I came home with 40.