Apparently I heard that George Washington still had a British accent because at the time, the American accent still haven't fully evolved. Later I heard that British accent was the one that evolved and the Brits sounded like modern day Americans.
Not to discourage further responses, but here are some good answers on the topic by other r/AskHistorians users:
When did Americans lose their British accents?, by u/keyilan
How did the American accent diverge from the British one? Did the founding fathers have British accents?, by u/YuunofYork
At what point did the accent of American settlers become distinguishable from a British accent?, by u/lord_mayor_pf_reddit