No 3.10-ig tudtam downgradelni, de allitolag az utolsó működő verzió az 1.80, viszont arra már azt mondja a flash utility hogy invalid file....
Just updating this since this thread comes up on Google in my searches for this board and IOMMU. As of 9.23.2019, ASrock has no working Ryzen 3000 BIOS's that support IOMMU. The last working BIOS for both the B450-Pro4 and B450M-Pro4 are 1.80, which only support Ryzen 1000/2000 CPUs.
On 9.17.2019 ASrock Support gave me a beta of 3.80 where they added a CBS feature of 'AEP CS' which did not fix the IOMMU issue.
FYI on 3.60 and 3.80 (as tested), BIOS Legacy Option ROMs are disabled by default now. This will prevent something like a LSI 9211-8i from posting (even in IT mode) and exposing its drives to the system BIOS. Enabling these under 'Boot Options' will enable the ROMs again.