Need to change settings in my.cnf
[mysqld]
default_authentication_plugin= mysql_native_password
Then login
$ docker-compose exec mysql bash
$ mysql -u root -p
(login as root)
ALTER USER 'root'@'localhost' IDENTIFIED WITH mysql_native_password BY 'secret';
ALTER USER 'root'@'%' IDENTIFIED WITH mysql_native_password BY 'secret';
ALTER USER 'default'@'%' IDENTIFIED WITH mysql_native_password BY 'secret';
then go to phpmyadmin and login as :
host -> mysql
user -> root
password -> secret