@Gord_Power
Unfortunate the DriveSmart 65 is not related (firmware-wise) to the nuvi 65 device discussed in the thread linked above. Your DS65 is Linux based rather than having the usual Garmin proprietary OS and firmware.

Even though you don't know the exact cause resulting in the boot failure, you've eliminated a corrupt firmware file (Garmin quite correctly refers to the firmware as 'software' in that example of "3. Recover from software failure"). So my guess is that it's been interrupted while the map update was being done via Garmin Express resulting in a corrupt/incomplete .IMG file loaded. Then when the device tries to load maps on start-up it fails to fully boot.

Unfortunately, with a Linux-based Garmin device case strongly suspecting the corrupt map file issue isn't helpful in being able to fix that issue. I don't know of any way to 'cure' Garmin's version of Linux firmware ("*.update") whereas with the proprietary fw ("*.gcd or *.rgn") several cure methods are well-known universally. If some Linux expert has worked that out they've not released it publicly. Without Mass Storage mode available it's also not possible to use a PC to simply remove any map .img file or format the internal memory and I see you clearly understand that already.

Perhaps it may successfully connect to a Linux computer?