The spinning circle lasted an eternity. Then, the text changed: "New version available: EMUI 12.0.0.XXX."
Therefore, the short answer is:
For users who cannot find the update via mobile data or Wi-Fi, using the Official Huawei HiSuite on a computer can often force a check for the latest stable build. Key Features of EMUI 12 huawei y9 prime 2019 emui 12 download