From the game's encyclopedia
Level of Devotion Impact increases or decreases the Modifiers gained from your current Level of Devotion.
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.
Level of Devotion Impact is an entry of Crusader Kings III's in-game encyclopedia. The game explains it: "Level of Devotion Impact increases or decreases the Modifiers gained from your current Level of Devotion." It is part of Level of Devotion. 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.