We normally discourage people from using non-server boards, especially gaming boards. They tend to have things that a NAS, (FreeNAS or other NAS), doesn't need. Like audio, WiFi or PC/2 keyboard & mouse port. Plus, they tend to use cheap Ethernet chips that perform poorly at full throughput, (which servers can often do). Server boards on the other hand, usually add IPMI / BMC which allows remote management, even at the BIOS level.
ASRock has a sub-brand called ASRock Rack which is for servers. If you are looking for a Mini-ITX board, you can filter here;
ASRock Rack Server boards
Plus, SuperMicro is popular for the build a server yourself crowd.
Now in regards to AMD processors for FreeNAS / TrueNAS Core, in the past it was recommended to use Intel processors. In the last few years, some AMD processors have both better performance and fewer CPU flaws inside. (Have to add my obligatory comment - compared to "Intel, the World's Leader in CPU Security Flaws"
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So, I have been looking at AMD Embedded Epyc server boards. Their are some nice ones, (both SuperMicro & ASRock Rack), that don't quite have all the built in ports I would prefer: Multi-Gig support, (1/2.5/5/10Gbps) and enough SATA or SAS ports, (I think 8 would be the minimum for a NAS board). So an add-on card for more SATA / SAS ports may be needed,
