My brother has a PC triple booted (windows, Fedora, Manjaro). After a resent update grub become severely damaged, namely his theme has disappeared, Manjaro freezes if booted from anything but the fallback image, and fedora shows up as multiple entries.
Despite the best of my efforts, nothing works.
I was wondering if formatting the EFI system partition, deleting the boot folders and reinstalling the bootloaders from a live USB is possible, and might help?
Welcome to the forum! 
Your topic title makes no sense as it reflects your imagined solution, not your actual problem. Classic XY Problem. Please edit it according to what you actually need help with.
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Thanks, will try this soon.