Asus announced in mid-July that it added support PCI-Express 4.0 to their AMD 400 series motherboards, a couple of days later, Biostar followed in his footsteps.
As soon as the month of August starts, Gigabyte removed such support on their AMD 300 and 400 series boards after launching a Beta BIOS, and it is now confirmed that the last AMD microcode, the AGESA ComboAM4 126.96.36.199ABB, will force all manufacturers to leave things as AMD wanted from the beginning: that PCI-Express 4.0 is an exclusive technology of their motherboards AMD X570.
The worst of all is that the company does not allow any partner to launch an updated BIOS that implements this compatibility.
In this way, the end user is the one who decides whether to maintain PCIe 4.0 support and buy an SSD that reaches a speed of up to 5000 MB / s, but will find that you cannot install any microcode update that involves solving future performance, compatibility or optimization problems of your system. So the user will have to choose between having the equipment in an optimal state by applying future updates, or getting stuck in a "Beta" version of their equipment to use a faster SSD, or of course, buying an AMD X570 motherboard to have both benefits, since after this software restriction, the new AMD platform is left with an extra feature.
According to AMD, they have made this move because they use a PCie 4.0 SSD could cause instability problems in the system, but today none of them has been replicated, in addition to manufacturers like Asus, depending on your motherboard, offered full or limited support to said interface to guarantee a correct functioning of the system, so it was no longer necessary to spend money on an X570 motherboard, until AMD has made an appearance.