Symfony 4国家字符编码

I have my old MySQL database with utf8 and utf8_general_ci - used in CakePHP 2.X. Now, I'm developing new version of my webportal in Symfony 4 (I'm new in Symfony).

Of course I use utf-8 in my template (twig) files.

I've changed Doctrine config file to use mysqli driver (I've found this solution in the internet) and utf8 instead of utf8mb4.

But still I have "?" symbols instead of my national characters such as "ń".

Do you have any idea? Thanks a lot.

EDIT:
I've checked that everywhere I have correct settings: I use utf8 (server, DB server, PHP, files etc.).