Just two hints that might be helpful here for your trip back:
– Always book the Hurtigruten Boat via the Norwegian website and pay in NOK. Don’t switch to English/global and just use Google translate. This will be about 30% cheaper. (Same goes for color line ferries btw.). Book here: https://www.hurtigruten.no/havn-til-havn
You can’t select a bicycle there (other vehicles you can). They told me that they always have space for a bike on those ships. You have to call them after you made the booking and they will add it. It’s about 100 NOK per day.

– If you fiddle with the Vy app, and check out different routes and such and stop a booking late in the booking process. Then 5 minutes later you want to actually book and you see no bicycle spaces there anymore and you say to yourself “Shoot, someone just snatched the last bicycle space while I was redeciding”. Chances are high that it’s not that but just you. The system keeps the bicycle space blocked for half an hour or so, to avoid double bookings (I guess). Wait for half an hour and your bicycle space is magically back. Same goes for normal seats btw. It’s just not really relevant there because there are plenty of seats but just a handful of bicycle spaces. You just get a different seat if you restart the booking.