[mass55th]

"If I recall correctly Kate and William did not wanna greet Trump or Melania."

I was under the impression it was Princess Anne who avoided the greeting line, not William and Kate.

[mass55th]

Kate Middleton was at the reception for the Trumps at Buckingham Palace in December 2019, but her husband wasn't:

Royal welcome for Trump: Donald and Melania Trump meet the Queen and Kate Middleton as Buckingham Palace hosts spectacular reception for Nato summit

He and Melania have met the Queen on three different occasions:

July 12–15, 2018: Met with Queen Elizabeth II and Prime Minister Theresa May. Spent weekend at his Turnberry golf resort in Scotland.

June 3–5, 2019: State Visit. Met with Queen Elizabeth II and Prime Minister Theresa May. Laid a wreath on the Tomb of the Unknown Warrior in Westminster Abbey. Attended the 75th anniversary of D-Day commemorative ceremonies.

December 2–4, 2019: Attended the 30th NATO summit. Met with Queen Elizabeth II and Prime Minister Boris Johnson. Also held bilateral meetings with Canadian prime minister Justin Trudeau, Danish prime minister Mette Frederiksen, French president Emmanuel Macron, German chancellor Angela Merkel and Italian prime minister Giuseppe Conte.