Can I use ECC memory in the 2019 Mac Pro?

Yes, but you must use the right kind. The 2019 Mac Pro requires RDIMMs or LRDIMMs — not unbuffered ECC DIMMs — and ECC memory is mandatory; the machine won’t boot without it. Stick to vendors like OWC or Crucial that explicitly list Mac Pro 2019 compatibility, and don’t mix capacities or speeds across channels.