Upgrade ssd in mac pro 2019

sorry, my response above was for MacBook Pro, not Mac Pro.

The Boot SSD in the 2019 Mac Pro is implemented as a matched pair of SSD data-only modules in proprietary slots connected to the mainboard. They are controlled by a Controller built into the T2 chip, and their update requires another Mac to negotiate the situation with the Mac Pro T2 chip software.

These are Apple Proprietary modules, not SSD Drives, and no third party modules are available at this writing.

The SSD storage components for the boot drive are soldered to the mainboard, and controlled by a Controller built into the T2 chip on the mainboard. You can not literally replace that boot drive.

If you would like to add an external drive, it can be Any interface you like, provided you can convert it back to one of the ports on your MacBook Pro.

USB-A and USB-C and Thunderbolt devices should be bootable in most cases.

Check requirements

To install or replace the SSD modules in your Mac Pro, here's what you need:

• T8 screwdriver
• USB-C to USB-C cable that supports both power and data
• Thunderbolt 3 cables aren’t supported.
• Another Mac computer with macOS 10.14.6 or later and Apple Configurator 2.12 or later
• SSD modules compatible with Mac Pro (2019)

from:

Install or replace SSD modules in your Mac Pro (2019) - Apple Support

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