Game concept
Struggle Catalyst
The game also links it as Catalyst, Catalysts.
From the game's encyclopedia
Struggles transition between Phases when certain notable actions are taken, building their Struggle Region's consensus towards a particular mood. A list of which actions are important in which Phase can be found in the Struggle window.
Example: the Opportunity Phase of the Iberian Struggle can transition into either the Hostility Phase or the Conciliation Phase. Murdering an important Character might work towards the former, whilst forming a Marriage Alliance with someone of a different Faith would build towards the latter.
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.
Struggle Catalyst is an entry of Crusader Kings III's in-game encyclopedia. The game explains it: "Struggles transition between Phases when certain notable actions are taken, building their Struggle Region's consensus towards a particular mood." It is part of Struggle. It covers Struggle Large Conquest. The game also links it as Catalyst and Catalysts. Patch 1.20.1.2, from game/common/game_concepts/03_fp2_game_concepts.txt and game/localization/english/game_concepts_l_english.yml.
Source: game/common/game_concepts/03_fp2_game_concepts.txt, game/localization/english/game_concepts_l_english.yml and the English localisation, Crusader Kings III 1.20.1.2.