I just want something small with ECC RAM

Not cheap, but does support ECC:

https://morefine.com/products/morefine-s500-mini-pc

The FAQ question reads a bit funny:

"Q19:Support ECC RAM？

YES. S500+ Support ECC RAM，

But compatibility requirements are higher, and cannot be used casually."

Also, these AsRock products:

https://www.asrockind.com/en-gb/4X4%20BOX-V1000M

https://www.asrockind.com/en-gb/4X4%20BOX-R1000M

Thank you for the links, that morefine one seems really nice, would need to get 2.5Gb networking gear...

I currently have a single 16 core/64 GB ECC Ryzen tower with ZFS that I'd like to break into a ZFS ARM ECC NFS server with a separate small form factor Ryzen or ARM compute cluster.

Honeycomb? https://www.solid-run.com/arm-servers-networking-platforms/h... I think they also have a lite version supporting ECC…