You'll need to be careful when deciding activities and locations as some places start shutting down for the summer season and others are not yet open for the winter season.
Here is a link that might get you started.
FjordTours things to do.
Are you planning to use mostly public transportation: trains, buses, ferries, planes? Or will you be renting a car?
If you decide to do the Norway in a Nutshell, try to overnight along the way so you are able to see the scenery during daylight hours.
FYI, Oct 26 Flåm Sunrise 7:42 am Sunset 4:48 pm
Hopefully someone with experience traveling in Norway late fall will chime in.
My trip to Norway was May/June 2023. We traveled from Kirkenes to Bergen on the Hurtigruten Coastal ferry. Then we spent a few days in both Bergen and Oslo traveling a DIY NIN in between with an overnight in Flåm. Then we flew to the art nouveau city of Ålesund for 3 nights where we cruised the Geirangerfjord one day and took a day tour to Trollstigen the next. Trollstigen usually closes sometime in October when the first heavy snows fall.
If you head north of the Arctic Circle you may have an opportunity to see the Northern Lights or do some whale watching. Maybe head to Tromso. Or spend the night in an ice hotel. Kirkenes has the Snow Hotel.
Hopefully, this will get you started with your plans. Congratulations!