If you like geometry I recommend problem 2 from that 1987 IMO. Simple formulation, elegant solution. Hard, but not crazy hard imo.

"In an acute-angled triangle ABC the interior bisector of the angle A intersects BC at L and intersects the circumcircle of ABC again at N. From point L perpendiculars are drawn to AB and AC, the feet of these perpendiculars being K and M respectively. Prove that the quadrilateral AKNM and the triangle ABC have equal areas."

Link to underlying link rather than to the quote-tweet spam:

https://xcancel.com/ruxandrateslo/status/1924206417000403328

  > @RuxandraTeslo: “I hadn't realized this but Romania's next president was 1st in the world in the International Maths Olympiad 2 years in a row with maximum score”

His name is Nicușor Dan. He was first in 1987 and 1988. https://wikipedia.org/wiki/Nicu%C8%99or_Dan