Is the “Explorer’s Guide to Wildemount” considered Official Dungeons&Dragons material?

“With the Explorer’s Guide to Wildemount announcement…” by Matthew Mercer

With the Explorer’s Guide to Wildemount announcement… from r/DnD

What is the typical wardrobe for someone in the Cobalt Soul?

Lycan: do the predatory strikes upgrade with character lvl?

Are the Warforged going to be possibly included in the world of Exandria? Either as NPC or potential PC race?

Why does the Dwendalian Empire have a King and not an Emperor?