MacBook Pro 2015 SSD corrupted(?) itself.

A Bare Metal Mac does not boot grub in response to its boot picker. It sounds like you have started to boot up your Linux install.

The classic way to take control back is to invoke the Mac ROM based Startup Manager, by holding the Alt/Option key at startup. This draws a gray screen, then over the course of the next few minutes, adds an Icon for every potentially MacOS or EFI bootable volume. when the wait timer disappears, it will be showing you the state of boot-ability based on all the drives it could inspect.

@Grant is correct and his suggestions will get you into macOS again. Once booted into macOS you can select macOS to be the default startup disk so that you end up using the Option Boot to access your Ubuntu installation.

Here is a bit of info regarding your options for attempting to fix the broken Ubuntu installation and some basics on how to use the GRUB interface.

The Ubuntu USB installer also has an option for attempting to fix Linux boot issues, or booting into a Linux recovery type mode with the installer where you can jump from the installer to the Ubuntu installation on the main drive where you can attempt to fix the Ubuntu boot issues. There are lots of articles and posts online on how to do this as it is too complicated to post here and much of it may require you to somehow determine what is wrong with your setup.

There are also instructions online regarding how to attempt to use the GRUB interface to attempt to boot the Ubuntu installation. It is a bit tricky to use the GRUB interface to manually boot the Linux installation, but it can be done. You need to tell GRUB where the root of the Ubuntu installation is which holds the initrd and Linux kernel files. You can use the "ls" command along with the partition items you listed to look for the correct partition & designation. After assigning the root to GRUB, you will need to point GRUB to the Linux kernel and initrd files in order to attempt booting the Ubuntu installation.

ls (hd1,gpt2)/

If (hd1,gpt2) is confirmed to be the Ubuntu root file system containing "vmlinuz" (link to the Linux kernel) and "initrd", then use this to set GRUB to default to it.

root=(hd1,gpt2)

Point to the Linux kernel & initrd files (sometimes with multiple kernel versions installed simultaneously there may be version numbers in the file names which may be needed, plus the versions must match as the kernel & initird are paired together...you can use Tab auto-completion to help out here). If the files are not there, then you may need to navigate to "/boot" or perhaps even "/boot/grub". There is also a possibility you may need to include kernel boot options or parameters....check the GRUB configuration file on that drive for what was setup as defaults.

kernel  /vmlinuz
initrd  /initrd.img

Now attempt to boot that kernel:

boot



Sometimes GRUB must be told to load other modules before being able to boot or even recognize the Linux root file system, but many times it can be this simple. Here is one article with some basic instructions for using the GRUB interface, there are probably some better articles out there:

https://www.linuxfoundation.org/blog/blog/classic-sysadmin-how-to-rescue-a-non-booting-grub-2-on-linux

FYI, I've gone through this multiple times over the years...each time I've had to search for information online on how to use the GRUB interface for some basic pointers. I've also reviewed my own GRUB configuration files to know what may be needed as options to the above commands. I think I wrote the instructions and examples correctly, but it has been some years now since I had to resort to using the GRUB interface (each system & installation can be unique).

I hope you have a good backup of your macOS installation just in case something catastrophic goes wrong.

I never recommend dual booting with the same drive as too many things can go wrong. Many people end up realizing much later that one or both partitions don't have enough room. It is much better to install Linux to an external USB3 SSD and leave the internal boot drive untouched. Now sometimes a Linux installer may place the Linux bootloader onto the internal drive, but if you can try having the Linux installer place the Linux bootloader on the external boot drive instead (also allows you to use that external Linux drive with other computers).

For many people installing Linux into a Virtual Machine may be more than sufficient depending on how you will be using Linux. This is the best option if it is suitable for your Linux workload since it is less likely to interfere with your macOS boot drive and it saves you from having to reboot in order to use Linux.

Also, since you are sharing the internal drive with macOS & Ubuntu, there is a third party graphical boot manager called "rEFInd" which can make it easier to boot to either OS without having to resort to Option Booting. Ubuntu may contain rEFInd in the main Ubuntu repositories (is available with my Debian installation), but I've never tried installing it from Linux before. Or it can be easily installed to the main internal drive through macOS. rEFInd actually is installed to the hidden ESP (aka EFI) partition. rEFInd can also work if installed on the internal drive to see external boot drives as long as the external drives are connected at boot.