Motherboard Asrock X570 phantom gaming 4

• Procesor AMD RYZEN 7 3800X 3.9/4.5 GHz, 8C/16T, Socket AM4
• DDR4 mem 32GB (2x16GB)

I can not run more than 2 GPU on that mobo.
Settings to run only 2 GPU : pbs pcie X16 =2x8 on Gen3
or 4x4 on Gen1

Any suggestion ? Link to see how to set BIOS for this mobo ? I have no idea any more.

usually the standard settings for a mobos BIOS are :
4G encoding enabled
PCIe bus set to GEN 2
secure boot off ( sometimes it causes problem with not loading something )