Travel bank can only be used for flights on Jetblue. If all goes as planned, Jetblue is expected to begin flying from Boston to London Stansted Airport in the summer of 2021. They have acquired slots to run two roundtrip flights per day, but it remains to be seen when they will begin service and what the frequency will be. They also have slots at London Gatwick for one daily roundtrip flight from JFK. The same caveats apply there. Both flights will have Jetblue Mint service (Business Class) which is very well regarded in the industry in its current iteration and supposedly being refreshed for their new TATL flights.

If you don't want to use the travel bank credit for yourself, you can always log in to your True Blue account and book some flights for someone else by applying the credit to those tickets. It's the perfect time of year to bestow a gift on someone else.