What you seem to be asking is whether, on Day 4 of 5 after the cruise, you should stay into the evening in Nuremberg for dinner and a night's sleep, or whether you should travel to Munich for dinner and a night's sleep.
Honestly, I don't think it matters much. Either way, you really don't gain much sightseeing time in one place or the other. I suppose if you leave Nuremberg in the pm on Day 4, you will need to check out in the morning and will have no access to your room in the afternoon, and you might need to fetch your bags from your hotel's front desk just prior to catching your train to Munich. Leave on the morning of Day 5 and it's more straightforward.
I don't find the "Nazi" stuff in Nuremberg all that interesting myself. Your time in Nuremberg is too short IMHO; Nuremberg has been around for hundreds and hundreds of years of course, and there is a large number of great sightseeing options that have nothing at all to do with that brief period when Nazis were trying to rule the planet.
https://tourismus.nuernberg.de/en/guidedtours/news/old-town-walking-tours-in-english/
https://museums.nuernberg.de/museum-for-industrial-culture
https://dbmuseum.de/en/nuremberg
https://tourismus.nuernberg.de/en/discover/places-of-interest/location/lorenzkirche-st-lawrence-church/
https://www.youtube.com/watch?v=mU7qmhO5uwM
https://tourismus.nuernberg.de/en/discover/places-of-interest/
https://www.tripadvisor.com/Attraction_Review-g187310-d241801-Reviews-Germanisches_Nationalmuseum-Nuremberg_Middle_Franconia_Franconia_Bavaria.html
https://www.tripadvisor.com/Attraction_Review-g187310-d659773-Reviews-Kaiserburg_Nurnberg-Nuremberg_Middle_Franconia_Franconia_Bavaria.html