There is no "/flash", not before nor after toggling the switch. Where should it be located exactly?
"rpi-eeprom-update -b" gives me "/boot", but nothing changes in that folder.
Oddly enough though "rpi-eeprom-update -l" gives me "/lib/firmware/raspberrypi/bootloader/default/pieeprom-2021-04-29.bin", not the expected "2022-01-25" version that shows in the settings. That version of the bin is nowhere to be found, not in critical, beta or stable. So it looks like it keeps staging the current version.
It would be good to confirm this if I know where the files are placed and if I can somehow capture the messages on the screen during boot.
EDIT
I double checked my build and the new files are included in the tar's SYSTEM file at "/usr/lib/kernel-overlays/base/lib/firmware/raspberrypi/bootloader/critical/", but not after flashing it in "/lib/firmware/raspberrypi/bootloader/critical/".
My gods, I feel like an idiot...the journal pointed out to me that I've been connecting to the wrong RPi...
I managed to take a photo of the messages after ten attempts. It's basically the same message as the output of performing "rpi-eeprom-update -a" manually.
*** INSTALLING EEPROM UPDATES ***
BOOTLOADER: update available
CURRENT: Thu Apr 29 16:11:25 UTC 2021 (1619712685)
LATEST: Tue Jan 25 14:30:41 UTC 2022 (1643121041)
RELEASE: default (/usr/lib/kernel-overlays/base/lib/firmware/raspberrypi/bootloader/default)
Use raspi-config to change the release.
VL805_FW: Using bootloader EEPROM
VL805: up to date
CURRENT: 000138a1
LATEST: 000138a1
CURRENT: Thu Apr 29 16:11:25 UTC 2021 (1619712685)
UPDATE: Tue Jan 25 14:30:41 UTC 2022 (1643121041)
BOOTFS: /flash
EEPROM updates pending. Please reboot to apply the update.
To cancel a pending update run "sudo rpi-eeprom-update -r".
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The contents of the /flash partition does not change when toggling the setting. This message tells me that it actually happens when performing the reboot. But the subsequent reboot does not manage to actually perform the update.
Staging the update manually through ssh, followed by a reboot, does update the firmware. I've got the latest up and running now. But this means the update through the settings is broken somehow.
Please let me know if/how I can perform additional analysis to get this fixed for others.