Well, yes, it is meant to boot Linux and anything else.
The problem is, GRUB (like many other bootloaders) does not fit into the small space normally reserved for a bootloader at the start of the disk. There are various ways you can solve this.
For Haiku BootManager, we use a few more sectors, and tell DriveSetup to not put any partitions there. BootManager installer will check that the needed space is free, too.
For some other bootloaders, they will create their own partition and store their data there.
For EFI bootloaders, this limitation doesnât exist. They are stored in files in the EFI partition and can be as large as you want.
But for GRUB? It usually has some files in your Linux system partition. Remove or corrupt that partition, and you now have an unbootable system that gives you only GRUB rescue mode. This problem is so bad that there is a live CD distribution dedicated entirely to fixing GRUB problems.
Is it bad? No, not really. Itâs a very flexible tool, possibly more than it really needs to, and will cover all possible corner cases. But that also means it is complicated to setup, or you have to rely on additional layers of software, such as os-prober, which will try to detect what OS you have installed and add them to a bunch of scripts that eventually generate a boot menu for GRUB.
You probably donât need all that. If you have GRUB because you use Linux anyways, yes, fine, no problem with that and your Linux install will take care of these things for you. But if you want to set it up standalone, without a companion Linux installation? Good luck.
On the other side, Haiku is going to need its own haiku_loader anyways. This one provides a friendly menu and allows to set various boot options. In order to get this friendliness, it loses some flexibility: it can only boot Haiku and nothing else. So you have to complement it with BootManager, or maybe with rEFInd for EFI systems, Itâs a different approach, one with tools that are less flexible, but easier to set up.