The error "File system check exit code is 8" indicates file system corruption on your Fusion Drive. To repair your Fusion drive, you need to reset it.
Remember to recover data from your Mac in Recovery Mode before proceeding, as the repair process will erase all data on the drive.
- Boot into macOS Recovery.
- Select Utilities > Terminal.
- Type the following command and hit Enter.diskutil resetFusion
- Type Y and hit Enter when prompted for a confirmation.
- Quit Terminal when the reset is complete.
- Click "Reinstall macOS" and follow the instructions to finish the installation.
