RESOLVED:
I chatted with one of the volunteers on SalemTechspert’s Discord (shoutout to Sim!) and he confirmed my suspicion that the BIOS was corrupted and I needed to flash the BIOS using an external programmer. I brought my laptop to a local laptop repair shop, provided them with a copy of the BIOS bin file extracted from the EFI Updater shell capsule file using UEFITool as well as a copy of the BIOS bin extracted from the exe installer (the latter was built by Sim). The technician desoldered the BIOS chip, reflashed the BIOS (he used the one that was extracted from the exe installer, but the one from the capsule file would have worked as well), soldered the chip back on, and the mainboard was successfully unbricked! I was very willing to pay the AUD$223 for this compared to having to buy a new mainboard under Framework Support’s recommendation (would also like to add that Framework Support did not tell me that a corrupt BIOS was the problem).
For anyone who can do some soldering work and have access to an external programmer such as the CH341A (with level conversion), you can probably do it for much cheaper! I have no soldering experience so did not want to take any chances doing it myself.
Feels good to save a mainboard.
This video is a good tutorial on how to do it (the BIOS chip used in this video is exactly the same chip on the Framework 16 7040 series mainboard - Winbond 25R256JWEQ). Part 2 of this series also tells you how to extract the BIOS bin from a capsule file.
I hope this helps someone!