If anyone suffered from sudden cut in electricity while the system is upgrading, this is how I solved it with help of this great community:
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Prepare a live USB containing Manjaro
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Boot into live mode and connect to internet
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In terminal type:
sudo su -
manjaro-chroot -a
Here select installed operating system that corresponds to Manjaro
pacman-mirrors --fasttrack
pacman -Syyu -
This is the important step that fixes the problem : you reinstall either the same version of the previous kernel or install new one (for me I chose 5.15):
pacman -S linux515 linux515-headers
Then reboot and happy Manjaro