In general some of the Intel Atom CPUs intended for embedded applications support the so-called In-Band ECC, where a part of the memory is reserved for storing ECC codes.
Two of the three ODROID H4 variants use the "Intel Processor N97" CPU, which is intended for embedded applications and it appears to support In-Band ECC, even if this is not clearly advertised on Intel Ark (i.e. at other CPUs of the Alder Lake N family, like i3-N305, at ECC Support it says "No", but at N97 it says neither "Yes" nor "No", but it is mentioned that it is intended for embedded applications, not for consumer applications, and the embedded models normally support In-Band ECC).
The ODROID H4 BIOS allows to enable In-Band ECC on ODROID H4 or ODROID H4+ (the latter is slightly more expensive at $139, but it has more I/O, including two 2.5 Gb/s Ethernet ports and four SATA ports; to the bare board you must add between $10 and $20 for the case, depending on its size, and a few other $ for SATA cables, RTC battery and optionally a cooling fan; you must also buy one 16 GB or 32 GB DDR5-4800 SODIMM, so after adding shipping and taxes a NAS would cost a little more than $200, besides the SSDs or HDDs).
From Unraid forum thread[1] there's links to another forum[2] and a wiki page[3]. Not yet sure myself what all of this means, but it looks interesting.
