I think the halakha is that you say a brocha seeing a monarch even when you are not a subject. You run to see him/her to appreciate a glimpse of power that is a small reflection of Hashem’s power.
Not sure about Americans. Maybe it is not appropriate of the colonies are still considered to be in rebellion. Not sure of treaty of Paris closed that chapter.
But to RR44, they are not reigning yet, so we should put it on record what we think of them now.