Short answers, pulled from the story.
Queen Anne vetoed the last Act of Parliament on the 11th of March 1708 by blocking the Scottish Militia Bill. This event marked the beginning of a centuries-long erosion of royal authority in the United Kingdom.
The Hittite people of ancient Anatolia established a constitutional monarchy where the king shared authority with an assembly called the Panku. This system functioned as a deliberative body similar to a modern legislature and dates back to the Bronze Age.
On the 11th of November 1975, the Governor-General dismissed Australian Prime Minister Gough Whitlam and installed Malcolm Fraser to resolve a budget deadlock. This exercise of reserve powers remains the most dramatic example of constitutional monarchy in action within the Commonwealth realms.
Poland adopted the first constitution for a monarchy on the 3rd of May 1791, which was the second single-document constitution in the world. This document followed the Constitution of the United States and established the Polish-Lithuanian Commonwealth as a republic under the presidency of the King.
King Bhumibol Adulyadej was the longest-reigning monarch in Thai history and reigned from 1946 until his death on the 13th of October 2016. He played an influential role in every political change during his reign and acted as a mediator between disputing political opponents.
Barbados declared a republic on the 30th of November 2021, ending its status as a constitutional monarchy in the Commonwealth of Nations. This transition is one of several examples of countries moving away from the constitutional monarchy model in recent years.