From the game's encyclopedia
The Wanua Government shares weaknesses with the Tribal Government, but also have reduced Domain Limit and Vassal Limit. While they use Gold to construct Buildings and recruit Men-at-Arms, they earn very little Gold from Buildings.
However, they can Barter GoodsBarter, Raid, and have synergies with the Mandala Government as they gain Legitimacy from being a Tributary.
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.
Wanua is an entry of Crusader Kings III's in-game encyclopedia (All Under Heaven). The game explains it: "The Wanua Government shares weaknesses with the Tribal Government, but also have reduced Domain Limit and Vassal Limit." The game also links it as Wanua Government. Patch 1.20.1.2, from game/common/game_concepts/tgp_game_concepts.txt and game/localization/english/game_concepts_l_english.yml.
Source: game/common/game_concepts/tgp_game_concepts.txt, game/localization/english/game_concepts_l_english.yml and the English localisation, Crusader Kings III 1.20.1.2.