They'll probably run in non-ECC mode.

Yes, they’ll likely boot, but the ECC functionality won’t work. The board will just treat them as regular DDR4 sticks.

ASRock B550 boards are hit or miss with ECC. Some BIOS revisions handle it silently, others refuse to post. Yours doesn’t list support, so you’re gambling. I’d bet it boots — most B550 boards with Ryzen CPUs ignore the ECC bits and run the memory in non-ECC mode. But I’ve seen a few where the system won’t even get to POST.

If you need actual error correction, buy a board that explicitly supports it. If you’re just trying to use spare RAM, give it a shot — worst case it doesn’t boot and you return them.