From the game's encyclopedia
An Interaction that allows Truces to be bought preemptively in exchange for GoldGold.
The game's text for patch 1.20.1.2. Words in blue are entries of the encyclopedia: hover one to read it, as in the game.
Purchase Truce is an entry of Crusader Kings III's in-game encyclopedia. The game explains it: "An Interaction that allows Truces to be bought preemptively in exchange for GoldGold." Patch 1.20.1.2, from game/common/game_concepts/00_game_concepts.txt and game/localization/english/game_concepts_l_english.yml.
for a guide, post or blog
Source: game/common/game_concepts/00_game_concepts.txt, game/localization/english/game_concepts_l_english.yml and the English localisation, Crusader Kings III 1.20.1.2.