'Baldur's Gate 3' mod allows multiclassing on its easiest difficulty
This difficulty level doesn't specifically say that the feature would be disabled, but a 'Baldur's Gate 3' modder has saved the day.
Gloomssassin Gloomstalker Ranger Swen Vincke Modder Thecomposer Gloomstalker Ranger Assassin Rogue Nexus Mods
Source: nme.com