Reports are that the foliage will be later this year. More toward the end of the month.

My travel buddy and I did that very thing in 2024. My favorite spot was Harvard Square. Many many outstanding museums there. (I can't pass up a museum, anywhere.) It was also fun to wander around and eat clam chowdrer, and drink beer at several cool pubs in the area.

I'd head to NH. The view from the back deck of the Mt Washington Resort is unparalleled. Whether you stay there or not, have a cup of tea there to enjoy the view. Take the cog train up to the top of the mountain. Take a boat ride on Lake Winnepesaukee. Head to Franconia Notch. See the waterfalls at Diana's Bath. If outlet shopping is your thing, you can do that in N. Conway too...esp if it's a rainy day. We stayed at Stonehurst Manor which includes breakfast and dinner. Mind you this was many years ago so things may have changed. But it's some thoughts about what we enjoyed when we were there.

The Isabella Stewart Gardner Museum, for sure. Also, there is a Duck Tour that is touristy, but fun--an amphibious vehicle that drives around Boston and then goes into the Charles River. The Freedom Trail is a red brick path on the sidewalk that takes you to all the historic sights and ends up at the Old North Church. I loved the Boston Public Garden. There are swan boat rides, and read Make Way for Ducklings before you go there. As you can see, I am a city girl. I can't help you with leaf peeping.

I found the Hop On - Hop Off bus to be an easy way to see Boston without driving everywhere or finding a place to park. We usually stay at the Fairmont Copley Plaza.

There is a great interactive map that predict fall color by date.

It's been pretty accurate. Boston would only be moderately colorful during those dates. You might see more spectacular foliage if you start in the north - say Vermont and then drive south.

https://www.explorefall.com/fall-foliage-map