ECC RAM won't run on a B660 board with an i5-12600K.

No.

Intel only supports ECC (unbuffered) on 12th-gen consumer CPUs when paired with a W680 chipset motherboard. B660 is a consumer chipset, and the BIOS/memory controller on those boards won’t enable ECC functions. Even if you plug in ECC DIMMs, they’ll likely run in non-ECC mode — or just not boot at all.

Some manufacturers might have a B660 board that technically allows ECC to work, but that’s rare and not something you should rely on. If you need error correction, get a W680 board or step up to a Xeon and a C-series chipset. Otherwise, regular DDR4/5 RAM is fine.