Stop between Boston and Prague

It's not halfway, but I stopped in Munich on the way to Prague in 2022. Munich is a calm airport in part because of its design.

I would also recommended the semi-recently-renovated Frankfort airport. This used to be among my least favorite airports in Europe, I didn't visit it in 13 years, then I passed through it 2015 and couldn't believe the upgrade.

The Dublin and Shannon, Ireland, airports wouldn't be bad.

Stop in Reykjavik, Iceland with Icelandair. They have stopover program.

Are you looking to stop for a few days? Just making sure I understand what you are asking.
You can work backward, using a site like SkyScanner to find flights to Prague. Then use Google to find the best direct flights to those possible locations from Boston.
Iceland is a great suggestion.

What do you mean by "stop"? Will you stay overnight and go to the airport a second time? If you have not visited Europe before, I suggest you go to the library, or buy any of our host's books like "Rick Steves .... name of country" for a lot of travel tips. There are a few top left of this page:
https://www.ricksteves.com/travel-tips

Most trips like Boston-Prague are decided by price or schedule availability. I would not introduce an extra stop into such a trip, and I've flown to Europe (from NYC) about 50 times. It may even cost extra to do what you are proposing. But current airport security procedures, and transport to and from airports makes me prefer a non-stop flight.

I will admit that a two segment flight (particularly with Lufthansa, because they partner with United, my frequent choice) is often cheaper, although it takes a little longer. But you can't get into your hotel room at 8AM (but only leave your bag with the porters ... ), so I don't mind arriving at noon or 1PM with a change of plane. But I don't find the trip less stressful because of the brief layover in a strange airport.

Prague is the kind of place that often does take a second flight segment whether you want it or not. So if you are proposing to add three days to your vacation, and stay in Berlin (?), you could even take a train to Prague, instead of schlepping to the airport again.

I take the British Airways day flight from Logan/Boston (7:25/8:25 AM depending on time of year) and fly into London’s Heathrow Terminal 5, arriving about 7:00 or 8:00 PM (easy 6 hour flight). I stay overnight at the Sofitel, which is a corridor walk from the terminal. (Oh, and I order room service.) The next day I fly to my destination in Europe, which has always been out of Terminal 5 as well on BA. You can do this heading home as well, and I will. It is so much nicer sleeping in a bed at night rather than on an airplane, IMO, and no jet lag exhaustion.

I have flown this route for years. For some reason I flew direct to Madrid this past May, over night, business class even. NEVER AGAIN. Sticking with my usual system from now on. It is easy and restful.

If you want to stop roughly halfway, the only option that is close to halfway is Reykjavík.

Thank you, very much your info is very much appreciated. Maybe someday I will be able to help someone.
Thanks,Deborah