As I have written before, I did sign up for the alpha as soon as I heard about it, but I have not yet received an email. Sigh. I have sent an email to Janet Lee, inquiring if I might still take part (although from this email it sounds as if they have already made their first selection of applicants).
And, by using the word alpha instead of beta, it sounds as if Facebook Horizon is still a bit rough around the edges. (When Sansar launched their invitation-only testing back in 2016, they called it a beta test.)
UPDATE 1:22 p.m.: Apparently, there was an alpha before the beta for Sansar, which was before my time.