After a long while I got a brief response from Asrock:
After checking with our engineer, X570 didn’t support Platform First Error handling (PFEH).
Which is a confusing statement, given that the option to toggle PFEH did exist in an early FW version (https://youtu.be/hus0u-jX6nc?t=312).
Are they just wrong or maybe the option to toggle it never actually did anything in versions where is was present?
Have you ever actually observed an error getting logged in dmesg? Maybe error reporting is working on the latest FW, despite the PFEH toggle missing. Another option that is visible, likely to be relevant is “MCA error thresh enable”. If no errors are getting reported to the OS, maybe messing with that setting could be the key.