OWC has unveiled its 64 or 128GB RAM stick kits for the new Mac Pro. They come in 768GB to 1.5TB SKUs, meaning a user can match Apple's factory maximum with this third-party memory. However, this option may also enable some savings.
https://www.notebookcheck.net/OWC-releases-its-max-outable-Mac-Pro-2019-RAM-upgrade-kits.448167.0.html