Game concept
Uninvolved
From the game's encyclopedia
For a Character to be considered Uninvolved in a particular Struggle, they need only have their Capital outside the Struggle Region.
This means they're considered an outsider, someone who not only doesn't have a serious stake in the ongoing Phases, but who shouldn't, because they clearly couldn't understand the local nuances.
As one of the only things people inside a Struggle can agree on is that Uninvolved Characters have no business in their lands, Uninvolved Rulers generally take harsh penalties in any Counties they hold within a Struggle Region.
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.
Uninvolved is an entry of Crusader Kings III's in-game encyclopedia. The game explains it: "For a Character to be considered Uninvolved in a particular Struggle, they need only have their Capital outside the Struggle Region." It is part of Struggle. 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.