Well said jackluke, (as he can't unmount volume for Disk Utility to run) while in SUM along with your recommendations is;Boot your Mojave disk in single user mode holding CMD+S after power-on and try these steps:
fsck -fy
mount -uw /
rm -R /System/Library/PrivateFrameworks/CoreBrightness.framework/Versions/A/CoreBrightness
cp -R /Users/YourUsername/CoreBrightness-backup/CoreBrightness.framework/Versions/A/ /System/Library/PrivateFrameworks/CoreBrightness.framework/Versions/A/
reboot
in this way you should boot Mojave at least in GUI mode, from there replace through Finder only this file I attached:
˜/sbin/fsck -fy
until "File System Was Modified" does NOT appear)