@mirabilos @mgorny I mean, linguistically, yes. In practice, no. I've asked (in English, with perhaps a bit of London accent) for porridge at a breakfast place in Hamburg. The waitress apologised that they only have Haferbrei and that I'm not going to like what I get. She wasn't wrong, it tasted like disappointment.
Porridge (and owsianka) are usually made by boiling rolled oats in water or milk, often with butter too, until it coagulates. Haferbrei is just hot water poured over oats 😭