There are a few…
Repair a non-booting GRUB – Discovery (endeavouros.com)
Grub: How to fix booting of other Arch-based systems? – Discovery (endeavouros.com)
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I linked to a couple of them further above but OP seemingly missed the “from the live session” part and attempted the recovery from their Mint install. And also mounting the wrong partitions at wrong places. Therefore the “reminder” and the spelling-out of the commands to run 
Updating your BIOS can cause some of your device identifiers to change so make sure whatever you are using to mount you volumes in /etc/fstab is still accurate.
They re-installed both their Linux systems 
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