BIOS version 4805 (and possibly older) has broken X2APIC mode, which in turn breaks amd-pstate support.
Other possible config values for APIC are Compatibility, Auto and XAPIC; best results were observed with XAPIC.
This is the error in dmesg when X2APIC is enabled:
amd_pstate: the _CPC object is not present in SBIOS or ACPI disabled
The IPMI is half-baked and for the most part unusable in a pure Linux environment, see https://forum.level1techs.com/t/remote-management-on-the-asus-pro-ws-x570-ace-under-linux
The groups are great, it's a good board for VFIO.
As stated on the product page, it works; explicitly enabling in BIOS might be required.
Tested with M391A2K43BB1-CTD.