There is two reasons for this , wrong root password or no root password
with this option disabled in the mysql settings , this is a workaround
for the second issue : 

sudo mysql -u root -p

Now you can alter root user password using the following cmd

ALTER USER 'root'@'localhost' IDENTIFIED BY 'password'

Remeber to change 'password' with your password 

and update it in the .env file of your application