I think he means that he has to activate XMP Profile to achieve the 3000mhz speed, otherwise it's recognized as being 2133mhz.
To OP: The (O.C.) which follows all the speeds listed indicates those are OverClocked speeds, which requires activating the XMP Profile. The Gigabyte Z390 Aorus Pro will not automatically operate your RAM at those speeds by default. Meaning that you will have to enable the XMP Profile from the system's UEFI BIOS. It's very easy to do, however.
When you boot the computer, press the Delete key while it's booting up to enter the BIOS. If you see the Aorus bird on your screen, start stabbing Delete & you should enter the BIOS if you were fast enough. If not, simply restart & this time be ready. You can spam...