So I received the invite for UCLA's preview day last week and have been waiting patiently for a status update, but since I've seen two letters posted on Reddit over the past couple of days by accepted students I just went for it and made a MyUCLA account with the UID given to me in the portal. From there, I got a "Congratulations on your admission to UCLA" message on the MyUCLA homepage with Political Science Fall 2025 listed as well. Unfortunately it won't let me access my financial aid letter at the moment but I'm hoping that'll start working once I can get the IT departments help on Monday.
TL;DR if you were invited to Preview Day but have had no official confirmation, just make a MyUCLA account!