Rental car or stick with public transportation?

I thought that driving in Norway was easy. Public transportation between certain points was great but some places are practically unreachable, (multiple transfers and potentially long layovers).

I’d drive.

That said, Bergen to Oslo has to be close to an 8-hour drive.

Helpful is the page "Getting around Norway".

Use https://entur.no/ to find public transport connections and https://www.vy.no/ for train connections.

Although there is not much traffic in Norway (except around cities) I would not entitle driving in Norway as "easy". There are some special challenges people shall know, e. g. animals on streets, using ferries, fast weather changes, different conditions on fjord and fjell level.

The official scenic routes of Norway help identifying worth seeing places.

I was driving the area multiple times and weeks with my own car.

It's very easy to do the route with trains and ferries. Train from Oslo to Ålesund, ferry from Ålesund to Bergen and then train from Bergen to Oslo. But if you plan to stay the last night at the airport my suggestion would be to do it in the other direction. Depending on what you're looking to see and do a rental car for part of the trip can also be an option.

Changed the original plans, and decided after 10 nights in capital cities (including one night on the Helsinki-Stockholm ferry), that renting a car for 3 days to get "out and about" was the best plan to chill, relax, and wind up our trip in Norway instead of staying in Bergen for two nights. Bergen is cute and I am sure it is a fun place, but...

We will drive from Oslo up to the Sognefjord area, see stave churches, take walks, enjoy nature. I wish I knew more about electric cars- their range, charging options, etc- but will stick with petrol for this trip. We live in the middle of nowhere, off gravel road and unmarked paved roads, without streetlights, and wildlife crossings are pretty much our norm. I don't plan on driving around in the dark anyway. Driving is not a concern.

Amazed how limited/sold out lodgings appear to be already on Booking.com for late September in Norway. I prefer to keep our lodging below $150 night and with only a couple exceptions, I met my goal. Was it Ben Green I saw on a RS Monday Travel who showed a glimpse of a spreadsheet he used to plan travel for a Scandinavia trip? That idea is brilliant (at least for me) and I have found it most handy. Definitely keeps all the information organized, and no financial surprises.

I also had range anxiety with respect to renting an electric car. I opted for the hybrid instead and everything was fine. Norway has an initiative to someday have all new cars be electric and there are many, many electric cars on the road. I bet it would have been ok to get the electric; but, I was on vacation and didn’t need any reason to fret.

Sounds like a good idea.

Using an e-car is of course a little change. Although the theoretic reach shrinks in hill and mountain areas, you will not drive more than 300 km per day in this area. So, one charge over night at hotels is sufficient for the reach of day. Hotels are well equipped with chargers.

More important to be aware of that they do no or only little artificial noise - therefore tourists at hotspots might walk infront of the e-car because they do not hear a motor moise.

Btw: what people in general shall know that e-cars are not allowed on Hurtigruten and Havila ships.

From experiences with own car I recommend the most comprehensive insurance because the likelihood for damages is higher than at some places.

Have a good planning and a good journey.

I wish I knew more about electric cars- their range, charging options,
etc- but will stick with petrol for this trip.

Electric cars are not that complicated and a modern car has enough range for you to not have to worry about it. A VW id.3 e.g. has, depending on model, between 400 and 600 km range. That should be more than enough for a normal tourist itinerary as long as you can charge overnight. And if a Norwegian hotel has parking, you can usually assume you can charge you car there. Electric cars are very much the norm in Norway and there are more electric cars then petrol cars in the country. And when looking at the data of new cars sold in Norway this year the vast majority are electric, petrol cars made up a grand total of 0.8% of all new cars. So even if you have booked an electric car you might get one.

And electric car will also save you money. Apart from petrol being expensive, electric cars usually get discounts on road tolls and ferry tolls.

Amazed how limited/sold out lodgings appear to be already on
Booking.com for late September in Norway. I prefer to keep our lodging
below $150 night and with only a couple exceptions, I met my goal.

Norway is not a cheap country. I don't know how much that is in kroner but looking at the individual hotel sites might save you a bit of money. Hostels can also be a good option.

Although the theoretic reach shrinks in hill and mountain areas,

Yes, but not by much. Going uphill requires a lot of energy, but you get much of it back when going downhill.

Btw: what people in general shall know that e-cars are not allowed on
Hurtigruten and Havila ships.

That is not true. Hurtigruten does not ban electric cars (couldn't find anything about it on Havila's website). Although I would not recommend bringing a car with you if you want travel part of Kystruten, it's probably cheaper to return the car when you board the ship and rent a new one when you arrive. (Although that is just a guess, and I might be wrong.)

We were there last year for 2 weeks. We took public transit for one week (including an overnight ferry from Bergen to Alesund) and rented a car for the second week. Both worked out great. The car was a hybrid Corolla. The roads were great and Norwegian drivers are very cautious and courteous. The only thing we had to get used to were the single lane roads where you had to keep your eye on the road way ahead and pull off if someone was coming. I don't think you'll encounter this too much where you are going.

We reserved a gas car but were upgraded to a hybrid. We got 47 MPG without ever using the optional plug in. I was happy with the hybrid, but I'm glad we didn't get an electric car.

We only took one fjord tour, but we were also on several ferries, so I felt that was enough time on the water.