You heard correctly, on July 31st 2021, Emirates Airlines and Alaska Airlines will no longer be partners. All tickets purchased before June 2nd 2021 “will earn miles as per usual for any dates already ticketed.”
This can be seen on Alaska Airlines Partnership page. Fly Emirates - Airline partners - Mileage Plan | Alaska Airlines
Our partnership with Emirates will end on July 31, 2021. Mileage Plan members can continue to earn and redeem* miles on one world® member airlines and our Global Partners to more than 1,000 destinations on 20+ airlines worldwide. For travel to India, the Middle East or Africa, guests can fly Qatar Airways in unparalleled comfort with their revolutionary Qsuite, the most private Business Class in the sky.
Alaska Airlines and Emirates Airlines have been partners for nearly a decade, this partnership started back in 2012. The partnership will come to a close on July 31st 2021, and effectively on August 1st, 2021, "the airlines will no longer have agreements covering codeshare, frequent flier programs and lounge cooperation."
This is sad to see and sad to hear, especially for Mileage program members of Alaska Airlines, because this is one less way to earn miles.
Please bare in mind, that Alaska Airlines have not changed anything else with non-Oneworld partners, for example Icelandair, El Al, and Singapore Airlines.