Reddit - Dive into anything is probably your best source. I have a ProArt X670E-CREATOR WIFI which also ECC runs happily on. In fact Asus have validated most of their boards with ECC support. It would’ve been nice if they could’ve stuck with Intel or Broadcom NICs instead of Aquantia but otherwise it’s a very nice board, long warranty (5 years) and a decent PCIe lane distribution between slots.
From all the research and motherboard manufacturers I have directly reached out to. The AMD5 does support ECC. The problem is the motherboard folks offer ECC - UNBUFFED support on their motherboard. None of them provide ECC - BUFFED (REGISTERED) support. If you want that kind of support, you must step to Xeon, Threadripper Pro, or Epyc.
I work in a CAD, 3D space and want ECC - BUFFED (REGISTERED) ram for the system’s stability.
So right now, what I see - the Xeon has MATX motherboard support with full ECC - BUFFED ram. I have found some of the AMD Epyc has some ITX motherboards will full ECC Support. And there are a few Threadripper Pros has full ECC support.