If you just want to buy something that'll "just work", The Lenovo P16[1], is ECC capable from the factory. Basically anything AMD "should" support ECC, it may need to be turned on in the bios. The problem with "should" is the trail-and-error you'll have to do to find a working combination, though, I personally I've never had many issues getting ECC working.
Note that AMD APUs prior to the 5000 series only supported ECC on the "PRO" models. For example, the Ryzen 3 PRO 3200G supports ECC, but the Ryzen 3 3200G doesn't.
