re-use internal SSD of 2019 Mac Pro

yes. you can first go to OWC’s website and find an appropriate drive enclosure. then once the drive is installed in the enclosure, you can erase and reformat it. then you can put it into service. please see Erase and reformat a storage device in Disk Utility on Mac - Apple Support

It is not clear to me that any aftermarket enclosures exist for the Mac Pro 2019 42 lb silver tower boot drive cards.

They are unusual in that there is no controller on board, only the SSD data arrays, so any enclosure would have to be specifically for that setup, and provide a controller.

The Mac Pro 2019 drive cards, and possibly the Mac studio drive cards, are a really unusual special case.

Your answer for ANY OTHER MacBook Pro boot drive cards was spot-on, because they are a variation of one type of SSD card with controller..

Grant Bennet-Alder wrote:

The Mac Pro 2019 drive cards, and possibly the Mac studio drive cards, are a really unusual special case.

that's good to know. I will file it in my grey matter. :) thanks again.

once again I learned something new. thanks. :)