Game concept
Promoted Legend
The game also links it as Promoting.
From the game's encyclopedia
A Promoted Legend is a Legend owned by a different Ruler that is being supported by Legend Promoters, who pay a monthly contribution to also get part of its bonuses.
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.
Promoted Legend is an entry of Crusader Kings III's in-game encyclopedia. The game explains it: "A Promoted Legend is a Legend owned by a different Ruler that is being supported by Legend Promoters, who pay a monthly contribution to also get part of its bonuses." It is part of Legend. The game also links it as Promoting. Patch 1.20.1.2, from game/common/game_concepts/06_ce1_game_concepts.txt and game/localization/english/game_concepts_l_english.yml.
Source: game/common/game_concepts/06_ce1_game_concepts.txt, game/localization/english/game_concepts_l_english.yml and the English localisation, Crusader Kings III 1.20.1.2.