Side Trip to Bayeux and Mont Saint Michel

Bayonne is in southwestern France. Do you mean Bayeux in Normandy?

You're right, Andrea. It was Bayeux. I realized my mistake and was just coming back to correct it. Thanks!

You can take a train from Paris to Bayeux. I stayed at Hotel Reine Mathilde and was very happy.
I then suggest booking a full day tour with Overlord tours. They also offer a one day trip to MSM.

Neither of these are easy/direct to get to from Paris CDG, if this is where you are arriving to. You will need to make one or more transfers. Expect it to take about 6 hours to get to Bayeux. A few hours longer for MSM.

I had this exact self pre tour planned for 2020 and had to cancel it all :-( Still have to reinstate my plans, but this is what I had planned:
Day 1 Arrive CDG,
Flat rate taxi to Gare St Lazare (cheaper option Roissy Bus/walk, but taxi plops you directly at station),
Train to Bayeaux (try to get direct, otherwise transfer in Caen),
I booked Hotel Churchill, but several other good options.
Days 1-3 Bayeux Tapestry museum (combo ticket includes small WW2/Normandy museum at edge of town and another small home/art museum). Bayeux Cathedral also on my list to see.
Day 3 I had pre booked Hotel Churchill's shuttle day tour (link on their website) to MSM. Arrives with the tourist hoards, but if you're travelling alone and don't want to rent a car, it seemed the logistically easiest way to visit.
Day 4 flex and/or return to Paris (I had goofed when counting days upon arrival so had an extra day, but a flex day could come in handy if MSM is closed for special event, or if you want to add Normandy Beaches tour.)
Bon Voyage!

When in Bayeux, check to see if there's a light show behind the cathedral. If so, don't miss it. It was truly spectacular!

I second the recommendation for Overlord tours. Taking the shuttle to MSM from the Churchill is the easiest way to go if you aren’t driving.

Thank you all for your recommendations and advice!