Need DFU procedure for 2019 Mac Pro 7,1

My Mac Pro 7,1 (2019) was bricked during an update from 15.4 to Tahoe. Password was not accepted post-install, different boot screens were presented between boots, machine was ultimately firmware locked, and had to be taken to a nearby authorized service center due to the closest Apple Store being hundreds of miles away. Tech there ran internet recovery, wiped the machine's onboard memory completely, and reinstalled OS 15. Machine booted but runs differently. For example, launching Disk Utility requires providing the same password twice; each boot presents desktop icons in different places; I was able to boot into Recovery Mode upon bringing the machine home, but after creating a new partition I can no longer do that. Recovery Assistant is all that's available in Recovery Mode. I'm persuaded that something elemental is wrong in the OS or the machine's OS-supporting substructure. Upshot is I can no longer trust that anything I do on the machine will be accessible or retained the next time I boot it. Therefore, I believe I need to restore it to its original specs, which seems to mean a DFU. I looked at the board's content and found info about that process regarding MacBook Pros and iMacs, but nothing about how it's done to a 2019 Mac Pro. Not interested in running Tahoe, but would like to install Sequoia again.