I’ve just come back from a long weekend in Oslo and only used my Monzo card and a bit of cash that I took as a backup and didn’t want to bring home with me.
I used the card for pretty much anything - coffee , supermarkets, airport, restaurants shops, even the Reuter app to buy tickets for public transport all worked fine. The Reuter app seemed to take a long time to accept the payment, but that may have been the app. I used both contactless and chip&pin without any problems.
Funnily, my ‘mainstream’ bank card got blocked while I was over there because I tried paying a large amount of money through PayPal (unrelated to me being abroad).
Glad I had my to rely on!