Start the Season 6 Season of Hatred quest FIRST. Season 6 quests are marked in BLUE. This kicks off in Zarbzinet and will direct you to fight a Realmwalker. More info later on this but the reward gives you a consumable 'Seething Opals' that have an XP buff and stack with Elixirs and Incense. You can then use these during the campaign.

The next Diablo 4 expansion is Vessel of Hatred, where we'll journey to Torajan Jungles (known to the locals as Nahantu) chasing after Neyrelle in a contin

In addition to a brand new story, tons of quality-of-life improvements, many new mechanics, and even some new endgame dungeons to enjoy, Diablo IV: Vessel Of Hatred also adds a new class; the Spiritborn.