How many days in Normandy

That depends on what you want to see and do there. If you have an interest in the D-Day sights, I highly recommend a full-day tour, so you start out needing two nights. That still leaves the sights in Bayeux (historic center, tapestry, cathedral, WW II museum), other WW II museums in the area that might be significant to folks with a serious interest in the subject, multiple picturesque towns to the east (Honfleur, Etretat, Deauville, Cabourg), Rouen, Mont-St-Michel, Giverny...

Heck, I spent 88 or 89 days in France in 2017 and didn't make it to Paris except to change trains. You have to choose between a more in-depth look at a few areas or a buffet approach. My personal philosophy is that I don't like spending significant time getting somewhere and then seeing only 10% or 20% of the sights. Other folks like to get an overview, figuring they can return later for more time in their favorite areas.

In my opinion, 3 days (4 nights) should be the minimum. We’ve trained to/from Bayeux, but found train to Caen is best if picking up/returning a rental car as the rental places are right outside the station. 15 min drive to Bayeux from there. In Bayeux you need a taxi to get to the only car rental place across town and very often you have to take the one and only car they have (it’s a gas station) despite what you reserved.
Bayeux is a wonderful, charming town and Normandy is amazing. We love driving the 2 lane roads from village to village exploring. So much to see and enjoy there.

We’ve stayed in Bayeux 6-7 times, a week each time, and still never want to leave.

We are staying in Bayeux and want to visit d day sites and museums. Could spend 1 week there if need be,

That’s extremely helpful with respect to getting train from Paris to Caen to rent car. We were cramming too much in initially. (Bruges, Normandy, Bordeaux,st Emilion, Lourdes, San Sebastián, Bilbao all by train). Are we crazy??????lol I guess at 73 we want to see as much as possible since we just retired and are pretty adventuresome.

I totally understand loretta, it’s so hard to choose places when you have limited time and hard to know how much time to budget for an area you’ve never been to. The D-Day sites, museums, and history is fascinating and that alone takes many days to do well. Then you add in the many wonderful towns, the Bayeux tapestry, the cathedral in Bayeux, the chateaux, etc, and a week is definitely not too long.