Crusader Kings III

In the start game menu, navigate to the 1066 start of Iberia In Pieces and choose King Alfonso VI of Leon in an Ironman game. You can challenge your brother, King Sancho II of Castille, to a board game for land right at the game start. I believe each character's stats are set where you have very high Intrigue and Sancho has high martial. Intrigue counters Martial in the chess mini-game, so just choosing the Intrigue option each time should result in your victory and the achievement will unlock.