@Joe_Ge
Reinstalling grub (grub-install --target=x86_64.efi --efi-directory=/boot/efi --bootloader-id=manjaro --recheck && update-grub) completed successfully. On rebooting, no change: still the initial four messages, then black screen.
I tried moving Boot option #6, [NVME:ESO512GYLCT-EP3-2L] to the top of the stack, using the BIOS Boot tab. Seems like that would have the effect of making the boot override option manjaro (ESO512GYLCT-EP3-2L) the default, so the system would boot normally without interrupting to display the BIOS menus and select the override. But the effect instead was to cause the boot process to fall through to boot the live environment from USB (still inserted and available), with the resulting environment showing no awareness of UEFI.
efibootmgr and the grub-install commands at this point showed the following from chroot:
[manjaro /]# efibootmgr
EFI variables are not supported on this system.
[manjaro /]# grub-install --target=x86_64-efi --efi-directory=/boot/efi --bootloader-id=manjaro --recheck
Installing for x86_64-efi platform.
EFI variables are not supported on this system.
EFI variables are not supported on this system.
grub-install: error: efibootmgr failed to register the boot entry: No such file or directory.
From the BIOS, I restored the boot order, returning the system to the previous status quo: booting to the installed OS only if I interrupt the boot process to override the boot option, selecting manjaro (ESO512GYLCT-EP3-2L).
I checked for differences between the primary EFI image and the fallback as suggested here: [root tip] [How To] Primer on handling a grub package update, and found that the timestamps were different. As recommended, I copied the grubx64.efi file over the bootx64.efi file.
The system is now booting up normally. Does that mean we’re finally done? It does seem like progress at least! Or is there more work to do?
As always, thanks so much for all your efforts on my behalf!