Actually I'm downloading it through origin now. I don't know if its working because I have EA Desktop installed as well (but not running at the same time), but I'm pre loading the beta using Origin and I have EA Play through GamePass.
If it helps anyone this is exactly what I did.
Went to the Origin.com WEBSITE and signed into the EA account that I have linked with my Xbox Gamepass account On that page is the 2042 beta with a pre load button, I clicked pre load (in my EA account "purchase history" it now shows BF 2042 beta). I then installed origin, and launched it but only with EA desktop not running. When I went to "My Game Library" the beta was there and it let me start pre loading.
I need to keep EA desktop installed because if I browse games in Origin, when I try to get a EA play game, it pull up the page to sub to EA Play or EA Play pro. But according to EA's FAQ you can have origin and EA desktop installed at the same time no problem you just can't RUN them both at the same time.