6 days in Scandinavia

Scandinavia is large and each of the mentioned destinations offer enough for a week.

Therefore I recommend to focus on two destinations, e. g. Copenhagen and Bergen.

Copenhagen is a very nice city and Roskilde's Viking Museum may interest you.

Stockholm is a little larger than Copenhagen and imo more functional. The Vasa Museum is fascinating and the staff is very helpful but basically around one core topic only.

Bergen is a nice small town but the main reason for a visit are the Western fjords behind or the start of a coastal cruise along Norway. A tour to Flåm and back you can plan with https://www.vy.no/en.

The Visit-pages of all three destinations present a lot of inspirations.

btw: Where in Friesland do you plan to bike (Netherlands and/or Germany?
Tip: Bike from West to East. There is a good reason why Dutch have Headwind Cycling Championships (Facebook link). :-)

Did you know that in Germany the North-Frisian islands are eastern of the East-Frisian islands? Also the old history of Frisians is very impressive but internationally fully undervalued.

Copenhagen, Stockholm and Bergen seem to me a bit too much to attempt in six days, though it is physically possible. Travel time between those places won't be insignificant.

I haven't been to Copenhagen for decades, but Stockholm is a lovely city with many interesting sights spread over a bunch of islands. It's not a place I'd want to go for just two days. From pre-trip research on Copenhagen, I feel the same way about that city. Bergen is worth at least a day by itself, and then the trip into the Sognefjord will take a day, because you'll want to take the Naeroyfjord ferry and the Flamsbana.

Thank you! I appreciate your responses. Some good suggestions and ideas. You're right to not try to do too much, but take time to enjoy and experience the sites.
LOL about the bike trip! I've heard about the headwinds. We are leaving Enkhuizen to Stavoren. Biking to Makkum, then boating to West Terschelling where we loop the island, then boating back to Harlingen, to Leeuwarden, Grouw, Sneek and back to Stavoren and Enkhuizen. It's a 7 day trip and it looks like half of it will be facing headwinds. Should be fun!!! Thanks for the warning!

Since you are experienced travellers on an introductory tour you already know what it's like to change hotels every other day. Bearing this in mind I would choose two destinations at most. Perhaps this is the time to visit and compare the two capitals.

Yes, I definitely know how hard it is changing hotels frequently. Good advice. That is what we’ll do. We can always do day trips if we want to spread out a little bit.