From the game's encyclopedia
A Casus Belli that allows a Ruler of the same Faith to declare War on an Excommunicated Emperor and destroy that Empire Title upon victory.
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.
Dissolve Empire is an entry of Crusader Kings III's in-game encyclopedia. The game explains it: "A Casus Belli that allows a Ruler of the same Faith to declare War on an Excommunicated Emperor and destroy that Empire Title upon victory." It is part of Casus Belli. Patch 1.20.1.2, from game/common/game_concepts/10_empire_faith_gate_game_concepts.txt and game/localization/english/game_concepts_l_english.yml.
Source: game/common/game_concepts/10_empire_faith_gate_game_concepts.txt, game/localization/english/game_concepts_l_english.yml and the English localisation, Crusader Kings III 1.20.1.2.