B450M Pro4 R2.0 ECC support

I actually own one of those motherboards, and ECC memory does work.
Whether error-correction works, my only experience is with B450 Gaming-ITX/ac, which had one corrected error recorded running FreeBSD. At that time, I was using Ryzen 3 PRO 2200GE. I have lots of AsRock AM4 boards with ECC memory, and I haven't seen any errors on any of them, which is sort of expected since most of them aren't 24/7 machines and I don't do all that much with them. Also, I have doubts about Windows reporting them correctly. Even if not reported correction should work.

Couple of things to remember:
1. Only unbufferred DIMMs will work. The last set I bought were directly from Crucial.com : MTA18ASF4G72AZ-3G2R
2. For APUs, only PRO versions work. This can get complicated because product naming is all over the place. For example, Ryzen 7 5700X (Vermeer) is a normal CPU, so it should work, but Ryzen 7 5700 (Cezanne) is an APU with iGPU disabled, so it won't work. Always check TechPowerUp specs page to make sure what you're getting.

Summit, Pinnacle, Matisse, Vermeer : All should work.
Raven, Picasso, Renoir, Cezanne : Only PRO version will work.