There are two requirements you must meet to unlock mounts in Diablo 4: Your character must be at least level 30, and you must complete the quest "Mount: Donan's Favour." This quest is not available in the beta version of the game. Once these requirements are met, you can get a mount from stables located in various areas of the Sanctuary, or as loot. It's worth noting that each mount in the game has its own upgrade system, allowing players to customise their preferred mode of transportation.