error: file ‘/boot/vmlinuz-5.12-X86-64’ not found on Manjaro grub after failed update.

 I am running Manjaro Linux since Sep 2020. There was a big update (larger than 1 GB) on 20th May 2021 and I left the Laptop after the update began.

After 30 minutes I found blank screen and could not even open a terminal by pressing Ctrl+Alt+F2. I pressed the power button to shutdown.

After restart I got the error: file ‘/boot/vmlinuz-5.12-X86-64’ not found you need to load the kernel first and could not proceed.

I logged in Ubuntu 20.04 and posted on Manjaro Forum and was asked to boot from Manjaro Live USB open the terminal and type:

[manjaro@manjaro ~]$ sudo su -
[manjaro ~]# manjaro-chroot -a
grub-probe: error: cannot find a GRUB drive for /dev/sdb1.  Check your device.map.
grub-probe: error: cannot find a GRUB drive for /dev/sdb1.  Check your device.map.
==> Detected systems:
 --> 0) Ubuntu
 --> 1) ManjaroLinux
==> Select system to mount [0-1] : 
1
==> Mounting (ManjaroLinux) [/dev/sda7]
 --> mount: [/mnt]
 --> mount: [/mnt/boot/efi]
[manjaro /]# rm -f /var/lib/pacman/db.lck
[manjaro /]# pacman -Syu
:: Synchronizing package databases...
 core is up to date
 extra                1910.3 KiB   498 KiB/s 00:04 [######################] 100%
 community is up to date
 multilib is up to date
:: Starting full system upgrade...
 there is nothing to do
[manjaro /]# 
It did not work.

Then I was asked to do:

# mkinitcpio -P

error no presets found

Then I was advised to list the installed kernels:

# mhwd-kernel -li 
and install at least one kernel
# mhwd-kernel -i linux510
I could not install linux510 but could install linux512

# mhwd-kernel -i linux512

After that I could login to installed Manjaro system using linux 5.12

I could reinstall linux510 through the same command on installed system.