I launch the game from the Blizzard Launcher and then it takes me into the game and if I press on create New it gives me this message:-
https://i.gyazo.com/62b6262199e114ec8ae6f11d42d6c05e.png
Unable to connect. You must launch Diablo II: Resurrected throught he Blizzard Battle.net Launcher.
Edit to add:-
Seems I should have read my email more carefully:-
Don’t miss your chance to pursue the mysterious Dark Wanderer and slay demonic hordes in the Diablo® II: Resurrected™ Technical Alpha. From now through April 11, cast, cleave, and shoot your way through the first two Acts of D2R as the spell-slinging Sorceress, the mighty Barbarian, and the keen-eyed Amazon.*