Game concept
Artifact Claim
The game also links it as Artifact Claims.
From the game's encyclopedia
An Artifact Claim represents someone's legal rights to an Artifact.
Having a Claim on an Artifact means that you can take various actions towards that artifact, and its owner, if you do not currently possess it (for example using the Steal Artifact Scheme).
There are Personal Artifact Claims for Character, and House Artifact Claims for Houses.
Artifact claims are simpler than those for Title Claims; they either exist, or they don't. They are also not inherited past the first generation.
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.
Artifact Claim is an entry of Crusader Kings III's in-game encyclopedia. The game explains it: "An Artifact Claim represents someone's legal rights to an Artifact." It is part of Artifact. It covers Personal Artifact Claim and House Artifact Claim. The game also links it as Artifact Claims. 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.