You might want to consider coming east. New England has some of the best vaccination rates in the country, and many great things to see and do, even from a scooter. Coming east through the Great Lakes are would be great. Madison, WI has great scenery around the University. Beautiful scenery, Niagra Falls, Tornado if Canada opens up, also Montreal. In NH, the white mountains are great. There are van rides up Mount Washington. Not sure if they can handle a scooter, but worth asking. Very close to the siteseeing overlook (maybe 150 feet). My idea of close is not what able bodied people say.
Vermont is lovely. The Green Mountains. The Maine Coast is gorgeous. Also fresh lobster right off the boat. Restaurants on the wharf, not fancy, best and not so pricy.
Massachusetts has tons of historical sites as well as many other sites, and restaurants… The Berkshires are nice, smaller mountains. Stockbridge is cute, but I don’t think you can get into Alice’s Restaurant. Nice to drive through the area. Tanglewood is a famous outdoor concert hall. I think there are no steps.
Boston can be challenging in old buildings but they’ve made efforts. Curb cuts everywhere.Many theaters and concerts. We went to see Hamilton - no elevators.Maybe the orchestra is possible. Check before buying tickets at all thesters, as they’re very expensive. Generally there are parking lots nearby. A couple of blocks, not very close. Check first if you want to take public transportation. The T (i.e. subway) is partially accessible. Not sure about buses.
Worcester is a smaller city, much better for driving and parking! There are excellent museums and restaurants, as well as a couple of theaters and sports events.
Salem is fun to visit. The Witch Museum is accessible, I think, as I remember ramps. They have tours of older sites. Even if you can’t get in, the history and information from the guides are worth doing.
Cape Cod, of course. Go on the weekend days, as weekend traffic can be awful in the summer. Ferries to Nantucket and Martha’s Vineyard it- unsure of accessibility. There’s a foot ferry from Boston to Provincetown, which is flat but old buildings… Lots of fun shopping.
There’s a good website called Only in Your State that has tons of resources. Wherever you go, have a wonderful vacation and birthday!