output from fsck_msdos :could not read boot block

Assuming an Intel Mac....Try booting into Recovery Mode (Command + R), or Internet Recovery Mode (Command + Option + R), or from a bootable macOS USB installer and see whether First Aid can repair the problem. If it cannot be repaired, then you will need to erase the drive and reinstall macOS followed by a restore from a backup. FYI, erasing a drive will destroy all data on the drive which was not previously backed up.