Ferry hopping without a plan
The best way to see the small islands of the Kattegat is to stop treating the ferry timetable as an obstacle. Most crossings run a handful of times a day, and in the off season the last boat leaves earlier than you would expect. Missing it is not a disaster. It is usually the start of the most interesting evening of the trip.
I have learned to pack as if I might stay one night longer than planned. A dry bag, a spare layer, a cheap headlamp and enough cash for a guesthouse that does not take cards. On the smaller islands the shop may close at five and the only warm place after dark is the harbour café, if it is open at all.
Ferries are also where you meet people. Farmers coming back from the mainland with a trailer of feed, teenagers going to school, a retired couple who have done the same crossing every Sunday for thirty years. Ask about the weather and you will get a better forecast than any app.