USB Worked OOB.
Everything you need is in the Dortania guide. You'll need an SSDT for B550 though, https://dortania.github.io/OpenCore-Install-Guide/troubleshooting/troubleshooting.html#stuck-at-acpi-table-loading-on-b550
Here we have the AMD OpenCore kernel patches for macOS Big Sur. These patches will boot macOS versions 10.13.x, 10.14.x, 10.15.x and 10.16.x (11.0.x)
We've stated these as Experimental as they could break between beta updates of macOS. Currently though they have worked since Public Beta 1...