Hello,
The "UNMOUNTABLE_BOOT_VOLUME" error is usually related to the failure of the operating system startup storage device (such as a hard drive). I see that you have tried the steps such as Startup Repair, bootrec command, and safe mode, but it still does not work.
It is recommended that you try to enter the command prompt in the Windows Recovery Environment and use CHKDSK /r to try to repair the file system.
If you cannot enter the Windows Recovery Environment, try to create a PE boot disk to enter the PE system to back up your data, and then contact MSI after-sales to detect the hard drive failure.