Blizzard has revealed that Vault of the Incarnates will exclusively use Group Loot, with no option for Personal Loot. Blizzard will be looking into feedback to improve the system before the release of Dragonflight.
While inside Vault of the Incarnates, Group Loot will be the only method of loot distribution. There is no option to select for yourself or your group to return to Personal Loot.
Some items, like professions reagents may still use Personal Loot where appropriate.