Any idea what to do with GNU GRUB 2.04?

Arash-Python wrote:

https://discussions.apple.com/content/attachment/38f339cd-d2a8-4b53-94b6-e17ec4cced76

Mac went off and not boot

This is dual Boot machine ...

Reboot holding the Option key to get to the Startup Disk Manager and choose your Macintosh HD

https://support.apple.com/en-us/HT202796#startupdisk

If no resolve boot to recovery—

Boot into Internet Recovery (Option Command R) and from the dropdown menu: Utilities>  Disk Utility> run the First Aid on your Macintosh HD (and the "Macintosh HD-Data" volume as well if Catalina/Big Sur) If errors are found and repaired, run again until no errors reported.

Disk Utility>View>Show All Devices The best sequence is —

• Volume level

• Container level

• Parent drive

Recovery: https://support.apple.com/en-us/HT204904

To fix a broken GRUB requires much more time & effort than I can give to you here on the forums. Depending on the reason for the failure sometimes it just isn't possible to boot the system from the broken GRUB configuration. Sometimes you will need to boot from your Linux USB installer many of which have a "recovery mode" type feature which can help you boot into either a limited Linux interface or allows you to jump into the broken Linux system so you can then use the tools on your broken Linux system to attempt to reinstall the boot loader, modify the configuration, or update the system. There are a lot of websites out there which explain how to use the GRUB interface to attempt to manually boot the system and how to use the "recovery mode" feature of the Linux installer. That is how I learned how to use the GRUB2 interface and to fix a broken Linux system.

While in the limited GRUB2 interface you can type "ls" to list the possible partitions/volumes. Then you can type "ls " again along with one of the partitions/volumes until you locate the one containing the Linux boot files which is usually located at "/boot" unless they are on a separate partition. For example if the Linux partition is (hd0, gpt2) and you type:

ls  (hd0,gpt2)

you should see the files on that Linux partition. Once you find the correct partition containing the Linux boot files you can then attempt to manually select the proper kernel and initrd images (and provide the proper kernel flags). Or you can try launching the GRUB2 menu (doubtful it will launch since you landed here). You will most likely need access to another working Linux system in order to examine the "/boot/grub.cfg" file for how to list the kernel and its flags. This is just something you will need to figure out by trial and error after reading about the GRUB2 interface.

I think booting your Linux installer in "recovery mode" is the best way to fix the boot issue or to boot into the broken Linux system.

However, you want to make sure your macOS volumes are backed up first just in case your attempts to fix the broken Linux system damages or corrupts the macOS portion of the drive.

Edit: @leroydouglas' suggestion will at least allow you to boot into macOS.