Normandy

I did the same in 2012: I toured Normandy, using Bayeux as my base.

Like you, I visited the D-Day sites via rental car and saw the all the key spots. Consider whether you want to go on a guided tour of the D-Day sites. I was told afterward that are excellent guides who specialize in D-Day, and they help bring the battle alive with detail and color. I wished I had gone on a tour instead. Whether you see the beaches by yourself or with a guide, don't miss Pointe du Hoc. That's the area where the Americans shot spikes into sheer cliffs and ascended them all under punishing fire. You can walk in bomb craters and German bunkers.

The Arromanches D-Day museum is excellent: https://musee-arromanches.fr/en/

The World War II museum in Caen is good, too: https://www.memorial-caen.com/

If you have time for only one of the two above, I'd go with Arromanches.

The Bayeux Tapestry Museum is a must: https://www.bayeuxmuseum.com/en/the-bayeux-tapestry/

Bayeux Cathedral is worth seeing.

I had a good restaurant in Bayeux, but I cannot remember the name.

Agree wholeheartedly with Graig's post.

Consider a stop along https://en.normandie-tourisme.fr/the-cider-route/ for a glass of cider or calvados. They don't grow many gapes in Normandy.
Visit the German cemetary in La Cambe for a stark contrast to the US Cemetary.
Have dinner there when you visit MSM. Try the salt-grass fed lamb at the Hotel du Guesclin if it is on offer. The dining room overlooks the ramparts.

I visit Normandy every other year right about that time. I hope you are aware that the anniversary of D-day is June 6th. Because of that, many places are much busier than usual (I hope you already have your accommodations reserved). There will be many ceremonies around that time, including a very large parachute drop on June 8th in Sainte-Mère-Église (active duty and reenactors). Looking at three nights, I am guessing only two full days? Mont Saint-Michel would occupy one of those days in its entirety, so that really leaves one full day for everything else. There are so many towns, sights, and museums in the area, and keep in mind that D-day is much more than the beaches themselves. Tell us what you are interested in seeing, and you will get much better recommendations. As far as restaurants, I would search this forum, where this topic comes up regularly, and make reservations for those days as soon as you are able.

I'm a big fan of taking a one-day D-Day tour if the visitor is not an expert on the subject.

The invasion museum in Bayeux is very good. It probably takes 2 hours or so for a pretty full visit. The Memorial de Caen museum isn't far from Bayeux but is really, really large. The exhibits start with the pre-war period and extend into the Cold War. I spent essentially the full day there and found it worthwhile. However, many people consider the museum too large, too expensive and too crowded. If you want a tight focus on what happened in Normandy during the war, the Memorial de Cean is probably not the right choice for you. It works better for folks spending a lot more time than average in the area, as I did.

There are many interesting places to go in Normandy, but your plate is already pretty full with Mont-St-Michel and the D-Day sites. If you tell us where you're driving from and later where you're headed after Bayeux (or after Mont-St-Michel?), you may get some suggestions for efficient stops along the way.

Karen,
Just to add to all the good advice here...On the day you are driving around the battlefields/beaches, end your day at the American Cemetery to witness the flag lowering ceremony. Info for that can be found at abmc.gov (American Battlefield Monuments Commission). They will possibly give you a time for the day you will be there. It is very moving, and the rows of crosses all lined up is never to be forgotten.
It appears you have two full days. As was mentioned, a trip to MSM will take up all of one of those days. Be sure to fit in the Bayeux tapestry at some point, probably first thing in the morning. It should take up about an hour total. Not sure about the cathedral hours, but if you can fit it in, go. The tapestry is being removed sometime in Sept. for some restoration work and will be unavailable for viewing for a good while.
Have a great trip!

Be sure to visit the Normandy American Cemetery. We took a free guided tour in English; it was excellent and very meaningful. You can email [email protected] for information about the tour schedule on the days you will be in town. The day we went, there was only one tour in English and we just happened to be there at the right time. Also give yourself plenty of time to see the exhibits at the Visitor Center.

Normandy American Cemetery
https://www.abmc.gov/about/normandy-american-cemetery/

Or, since you're going to be at Mont-Saint-Michel anyway, consider stopping at the Brittany-American Cemetery in Saint-James, a short drive (20 minutes) from MSM.

Despite its name, it's located in Normandie.

I haven't tried it yet, but the well-known cookware manufacturer Mauviel1830 opened in January of this year a new gastronomic restaurant at le Logis Sainte-Catherine at Mont-Saint-Michel, headed by Michelin-starred chef Jean Imbert. Given the generally mediocre offerings available at the Mont's restaurants, it's a welcome addition. You might want to check it out.