President Trump & 1st Lady did not curtsy or bow to the Queen. Good for them. They are not subjects and are not obligated to do that. Some in the press bemoaned them for that. But they are Americans and no American should be expected to bow to anyone.
Anytime I hear one of these stories about an American president not giving the "royals" the curtsy or bow I think of three dates 1776, 1941, and 1945