Tour of Scandinavia in July

The only time I needed cash on a RS Scandinavia tour to those 3 countries was for a laundromat in Copenhagen.

Do we really need NO cash, is Apple Pay advisable - or only credit cards necessary?

I have used Apple Pay almost exclusively over the last 5-7 years in Germany, the Netherlands, Belgium, Scotland, England and Paris. My trip last year in England lasted for 6 weeks and I only used cash once (and that was an unusual situation).

From from everything I've read, Scandinavia is more cashless than anyplace else.

I understand your concern. We usually travel with a bit of cash, but decided to go cash free in Norway in 2023. We never used cash at all in our 2 and a half weeks with the exception of needing a few Krone for the laundry on our Hurtigruten ship. Fortunately, reception gave me the coins and just billed our cabin.

If cashless, how do you leave a tip for the hotel cleaning staff at the end of your stay?

I'm sure our Scandinavian posters will correct me if I am wrong, but I don't believe tipping housekeeping in these countries is the norm. Scandinavia is not a tipping society and hotel employees are paid a good wage.

Norway is so cashless that in 2023 I had a very difficult time finding a bank-owned ATM. The one I eventually encountered had a long line of people (I think at least 10) waiting to use it. Many, many Norwegian business have "No cash" signs posted. It's likely you won't need any cash at all in Norway. The two places I needed cash (during a 3-week trip) were really obscure.

I encountered a street-food stand in Sweden that accepted only cash and a local fund-transfer app I wasn't familiar with, but otherwise I could probably have used a credit card everywhere in Sweden.

I'm always a bit uncomfortable pulling out a card in a little corner store if I'm just buying a banana or a Coke. Occasionally one of those places (almost certainly not in Norway) will have a minimum-purchase requirement for credit card use.