Ryzen Threadripper and the TR4 socket are advertised with ECC support on the AMD website¹², in contrast to regular Ryzen/AM4. This may mean that all motherboards support it. I can't be sure, however, ECC seems to work fine on ASRock X399 Taichi.

¹ https://www.amd.com/en/products/ryzen-threadripper ² https://www.amd.com/en/products/str4-platform