Feel like I've hit a dead end. Thanks to @Renate

I now have the tools to troubleshoot and have learned a lot about what makes these things tick. I've tried many ways to revive the device and it's not responding as expected. If the Google AI response is accurate, it's unable to load and draw the recovery menu to the screen as a result of faulty recovery partition and/or problem with the bootloader.
A factory reset when done against a root-patched image running Magisk (this was back in 2023) could have corrupted an area or partition unexpectedly...Onyx factory reset going against a root-patched device yielded a busted device
Q: Is it possible the firehose file is not the correct one? Or would we have seen an error immediately if it wasn't compatible?
Q: Would an update.gpx at version 3.3.1 or 3.3.2 make any difference?