Well, isn't this a funny one.
Foreign heads of state are under no obligation to respect protocols of foreign royalty, particularly in their own country.
Seems Camilla didn't get the memo:
"Queen Camilla, 76, and Brigitte, 71, had an awkward moment on June 6 during a service marking the 80th anniversary of the D-Day Landings in Normandy, France. As seen in a video shared to X by the Daily Mail, French President Emmanuel Macron's wife tried to hold the royal's hand after they laid wreaths at the British Normandy Memorial at Ver-sur-Mer. However, Queen Camilla didn't reciprocate, keeping her arm at her side. After briefly grasping the royal's hand, Brigitte stepped to the side and folded her arms in front of her.
Proper etiquette around interacting with the British royals has long been a highly discussed subject. The royal family's website, which has yet to be updated in full following the death of Queen Elizabeth in September 2022, states, "There are no obligatory codes of behavior when meeting The Queen or a member of the royal family, but many people wish to observe the traditional forms."
Funnily enough, Charles himself didn't follow royal protocol:
"Proving that there are no hard and fast rules around how to say hello, King Charles, 75, greeted President Macron with a hug at the British Normandy Memorial and kissed his wife's hand."
I guess Camilla's more royal than the royals themselves?
https://people.com/queen-camilla-brigitte-macron-awkward-moment-royal-avoids-holding-hands-d-day-anniversary-event-france-8659266