ECC support works, reporting to the OS works - both single and dual bit errors. If you have issues under windows then that’s windows fault. ECC reporting is just a bunch of registers/interrupts - much lower in the HW stack then the OS itself. The OS just needs to be able to read/interpret what the CPU is saying.
What doesn’t work is the reporting by the IPMI on those boards.
My theory is that asrock is under embargo/mandate from AMD that prevents them from declaring full ECC support on non-epyc cpus. Or simply amd does not provide asrock with everything they need for full support validation. (market segmentation)