The latest Diablo IV quarterly update reveals that the development process was not really affected by the pandemic and also details key game aspects like storytelling, open world, multiplayer and itemization. No ETA for the Alpha and Beta tests as of yet, but there will be another update around BlizzCon.
https://www.notebookcheck.net/Diablo-IV-development-chugging-along-nicely-new-game-details-unveiled.477523.0.html