So far, Blizzard has only revealed that the beta testing for Diablo II: Resurrected will take place this month. There is actually no official date yet. However, Microsoft could have betrayed this in its own store.
As several pages reported over the weekend, Microsoft has meanwhile published the 17th on the shop page for the Diablo II: Resurrected Beta August 2021 named as the release date. The date has been removed in the meantime, but screenshots prove its existence.
Whether the date true or not, remains to be seen. Since a community manager from Blizzard indicated two different “weekends” for the two beta phases (first closed beta, then open beta) in advance, August 17th does not quite fit into the picture, as it would be a Tuesday.
There is speculation in the Blizzard forum that August 17th could mark the start of the open beta, while the closed beta for pre-orderers could start the weekend before: Friday August 13, 2021 would not be a bad date for the hellish game, which will officially be released on September 23, 2021.