Long version - my DM (Prod) has always served bread sauce with Christmas dinner when I was a child. Sometimes we would go to Dad's side of the family (Catholic) for Christmas dinner and I can't remember clearly whether we had bread sauce then or not, but I think we did. Certainly when they came to us there weren't any comments about Mum serving bread sauce, but perhaps they were being polite.
This morning DH was shopping in Dunnes and there was no bread sauce, I wanted fresh but would have accepted packet mix, but nothing at all. He asked a couple of employees but they had never heard of it, however they weren't Irish so it could just be something that they're not aware of.
DH (Asian, so thinks a sauce made from bread is weird and unnecessary) was on a video chat with his friend when I walked into the room and he told me that he couldn't find it. His friend (Irish Catholic) had no idea what bread sauce was either, he's the one that suggested it's a Proddy thing. When I thought about it I realised that I had only ever bought fresh bread sauce from M&S, so imported into Ireland, but I still feel like I've seen packet bread sauce around in other places too.
So, which is it?
a) Everyone knows and uses bread sauce
b) It's just for Protestants
c) Condiments don't have a religious affiliation
d) Only a slattern would buy it instead of making it herself.