Game concept
Ruined Building
The game also links it as Ruined.
From the game's encyclopedia
A building that has been Ruined has been shattered, defaced or pillaged for parts by external forces.
These external forces might be things like:
• Vengeful Mandala Rulers
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.
Ruined Building is an entry of Crusader Kings III's in-game encyclopedia. The game explains it: "A building that has been Ruined has been shattered, defaced or pillaged for parts by external forces." It is part of Great Building. The game also links it as Ruined. Patch 1.20.1.2, from game/common/game_concepts/00_game_concepts.txt and game/localization/english/game_concepts_l_english.yml.
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.