Fix 'Warning: os-prober will not be executed to detect other bootable partitions' grub issue:
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Edit the /etc/default/grub file and add this line:
GRUB_DISABLE_OS_PROBER=false

save the file and run update-grub again.


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Source: https://askubuntu.com/questions/1414245/why-do-i-get-warning-os-prober-will-not-be-executed-to-detect-other-bootable-p
Date: Feb 17th 2023