Yeah only the first AC game “celebrated” 4th of July. For that game, that day was the only day other than New Years that you could catch the fireworks I believe. After that game the fireworks show moved to a weekly August event with no mention of 4th of July.
That being said, Explorer’s Day has always coincided with Columbus Day, which IS an American Holiday. While Columbus Day is quickly being replaced or cancelled IRL. Idk if that means it will be in ACNH since it’s not an exact replica of the holiday.