No, Grub will not overwrite the Windows Boot Manager.
No, Grub will not overwrite the Windows Boot Manager.
This happens because the Windows boot manager doesn't support Linux directly, while GRUB can handle both Linux and Windows. To fix it, use two hard drives—one with Linux and one with Windows—and set the Windows drive as the default boot option in your BIOS. Only then will you be able to start Linux.
The question highlights confusion about having two distinct boot managers on the EFI partition. It seeks clarity on why such a setup isn't possible or allowed.
Bios often let you pick which boot manager to use for a drive, but finding the right option can be tricky. You might need to do some advanced partition work to ensure everything runs properly. Doing this yourself isn’t safe—losing data or bricking your OS is possible. I usually keep my Linux and Windows separate, especially when dual-booting on a shared drive. Avoid messing with partitions; it’s better to be cautious. Some people have heard scary stories about Windows tools accidentally wiping Linux partitions, so it’s wise to stick with caution.
The BIOS handles booting at a physical level only. The boot manager decides which operating system starts on a logical level. Having multiple boot managers on one drive isn’t practical, so you’d need a pre-boot manager. That would require two drives and using the BIOS to change between them. The BIOS just loads whatever is selected on the chosen drive, without understanding specifics like GRUB.
I tested it in a VM and everything worked easily. Initially I mounted the whole drive with Windows installed, then reduced the main partition to fit Linux. After that I installed Linux on the freed space. GRUB became the default bootloader, but I switched BIOS order so WBM came first. Now the system boots straight into Windows without any prompt, and to start Linux I just need to use the BIOS menu. This process was very simple—why did you assume it couldn't support two boot managers on the same drive? Once it's done, I'm wondering what I should do to keep both managers stable. I've heard Windows and sometimes even Linux can overwrite each other's boot entries, but I believe Linux is manageable. There seems to be a setting in GRUB's configuration that handles this, though I'm not sure about Windows. I won't be upset if GRUB gets corrupted, as I don't update it often.
It seems like you're testing on a virtual environment. Try using it on actual storage. If it functions, you're welcome.
It's clear you're comfortable navigating your BIOS options. You prefer using the UEFI OS or Windows Boot Manager for easier access to Grub. Instead of pressing F11 during startup, you simply wait for Grub to appear and choose between Windows and Linux. This method has been reliable on your system since 2021, and you've successfully used it on previous setups with Windows versions ranging from 7 to 10. You didn't encounter any problems with updates while using this approach.
It's possible in theory, though it might seem overly repetitive.