Starting with mysql 8.0 the default authentication plugin was changed from mysql_native_password
to caching_sha2_password
where a lot of clients (phpmyadmin) might have problems with. If you run into this problem and your client app can not handle the new method simple use a 7.x version of mysql.
https://dev.mysql.com/doc/refman/8.0/en/caching-sha2-pluggable-authentication.html