Navicat无法连接MySQL8.0的原因是因为加密规则比较严格，因此只需要登陆mysql的终端进行修改命令即可

251 - Client does not support authentication protocol requested by server; consider upgrading MySQL client

解决办法：登录之后

4、更改加密方式：

mysql> ALTER USER 'root'@'localhost' IDENTIFIED BY 'password' PASSWORD EXPIRE NEVER;

5、更改密码：该例子中 123为新密码

mysql> ALTER USER 'root'@'localhost' IDENTIFIED WITH mysql_native_password BY '123456';

6、刷新：

mysql> FLUSH PRIVILEGES;