Thank you, so the problem is that MySQL 8.0 uses a different authentication plugin, not supported by MariaDB client used in the Valentina Studio.
Here's the discussion
https://stackoverflow.com/questions/49194719/authentication-plugin-caching-sha2-password-cannot-be-loaded
While it is not supported and we're working on fixing it, you can create a new user which uses an older plugin
CREATE USER 'username'@'ip_address' IDENTIFIED WITH mysql_native_password BY 'user_password';
Or alter an existing
ALTER USER 'username'@'ip_address' IDENTIFIED WITH mysql_native_password BY 'user_password';