The designated data directory /usr/local/var/mysql/ is unusable. You can remove all files that the server added to it. code example
Example: brew reinstall mysql
# To uninstall
brew uninstall [email protected]
rm -rf /usr/local/var/mysql
rm /usr/local/etc/my.cnf
# To Reinstall
brew install [email protected]
brew link --force [email protected]
brew services start [email protected]