Seconded, but hard to find for small boxes. I have seen in-band ECC on Asus Nucs, but that is as good as it gets from what I can tell.

There is the new Minisforum N5 Pro, which supports DDR5 ECC RAM. I'm keeping an eye on it.

totally agree. That's why my homelab storage server(s) are 2nd hand enterprise machines. They come with ECC.

True! Unfortunately, an enterprise machine is more likely to have considerable power draw and quite possibly be much louder. I have a 2013 Apple Mac Pro (trashcan) that uses ECC. They're also cheap, small, and quiet.

I'm not too familiar with it. Why do you want or need ECC RAM for your homelab?

ECC RAM protects against bit flips (a bit changing to the wrong state). These can be caused by electric or magnetic interference. A pixel of a picture suddenly having the wrong color because of a bit flip is not that bad but some day an important file might end up corrupted because of one. I want to sleep well at night not having to worry about silent data corruption so ECC RAM it is. See here for more information: https://en.wikipedia.org/wiki/ECC_memory