How can I solve this problem? ... create a connection in webmin, but when I want to access the MySQL database of webmin, it shows me a message with a startup failure ... I put the password of my root and mysql and I still can not login, I would appreciate your response. Thanks .. 
You can change the encryption of the user's password by altering the user with the following Alter command:
ALTER USER 'username' @ 'ip_address' IDENTIFIED WITH mysql_native_password BY 'password';
We can avoid this error by making it work with the old password plugin:
First change the authentication plug-in in the my.cnf file for the Linux file / my.ini in Windows.
[mysqld]
default_authentication_plugin = mysql_native_password
Restart the mysql server to make changes in effect and try to connect through MySQL with any mysql client.
If you still can not connect and you get the following error:
Unable to load plugin 'caching_sha2_password'
It means that your user needs the previous plugin. Therefore, try to create a new user with the create user or the grant command after changing the default plugin. then the new user needs the native plugin and can connect to MySQL.
Author of the response: love aggarwal
the original question is: authentication plugin caching sha2 password can not be loaded