AMD’s latest AGESA update, AGESA AM4 1.0.0.3 ABB, will axe any PCIe 4.0 functionality on non-X570 AM4 boards. This is due to a handful of rogue motherboard vendors implementing PCIe 4.0 support on older motherboards, albeit in limited form. In addition to removing any added PCIe support for older motherboards, the new AGESA update also includes fixes for Destiny 2, which has*been a problem*for early adopters of Ryzen 3000.
AMD officially told us at Computex that it intended to eventually kill PCIe 4.0 support. We’ve had some motherboard manufacturers tell us that, theoretically, they would be able to reverse engineer the AGESA binary provided by AMD and re-enable PCIe 4.0, but it’s just a question of if anyone actually does that. The code is provided as binary and isn’t explained or detailed beyond what’s provided, so a company would have to go through and toggle bits until they find the PCIe 4.0 support.
Using an older AGESA would allow you to continue using PCIe Gen4 on boards where it was temporarily supported, but then you’d lose other fixes in AGESA code, like the Destiny fixes.