From the mysql documentation version: 8.0.18:
A superuser account 'root'@'localhost'
is created. A password for the superuser is set and stored
in the error log file. To reveal it, use the following command:
shell> sudo grep 'temporary password' /var/log/mysqld.log
Change the root password as soon as possible by logging in with the generated, temporary password
and set a custom password for the superuser account:
shell> mysql -uroot -p
mysql> ALTER USER 'root'@'localhost' IDENTIFIED BY 'MyNewPass4!';