OsxAptioFix2Drv-free2000.efi has been effective on just about all Gigabyte Z390 boards in combination with slide=0 (in Boot Arguments). If you search the site for this driver name you will find that it's used successfully on other manufacturer's boards as well.
Choosing a memory fix driver for a particular motherboard is a trial-and-error process. We start with AptioMemoryFix-64 and, if it fails, we switch it out for a different one.
On the Designare Z390, AptioMemoryFix-64 actually works. When we install a GPU into slot 1 (maybe even slot 2) is still works. But when we subsequently install a WiFi/BT card, it completely crashes. All other memory drivers also crash with the sole exception of OsxAptioFix2Drv-free2000.