Editing /etc/default/grub is a very standard way to configure GRUB. It is explicitly designed for user modification, and the GRUB_DISABLE_OS_PROBER=false option is a documented setting.
I know many people have a knee-jerk reaction - editing system files can feel intimidating… But… any changes in this file are pretty low-risk - you’re only uncommenting existing options with the file being backed up by grub-mkconfig or update-grub.
Having used Linux since Ubuntu Hardy Heron many moons ago, I would definitely go into this file and check it’s contents whatever distribution I had installed - though for more casual users or noobs it generally only needs checking out if there’s some kind of issue.
Manjaro (like Arch and other derivatives) does not enable os-prober by default as of recent updates, and this is intentional due to security concerns.
This tool mounts all partitions to detect other OSes, which could exploit filesystem vulnerabiltities or insecure configurations - especially under Secure Boot scenarios.
The change was adopted (not by Manjaro) by upstream GRUB developers.
From 2021: GRUB2: Why is OS-Prober now disabled by default?
As usual, a quick search will reveal quite a few topics about it, with a few nOObs complaining that they would expect automatic detection.
The only criticisms mostly come from Windows users who are accustomed to an operating system which prefers to be insecure by default and by design…
It could be said that Manjaro could improve this in a couple of ways:
- Documenting the change prominently during installation
- Adding a GUI toggle (e.g. in GRUB settings) to simplify the process.
Personally, I would ONLY enable this option when setting up a dual-boot - and I would disable it when finished.
This comment is inflammatory - so @anon33601770 made a valid comment there.