Form-Action Variables not working while routing

Hi everyone,
it looks like my CI4 does not process form variables.

I have a very simple form with an action to "/login/" for example.

goes like this:
helper(['form', 'url']);
echo form_open('/login/user_login_process/');
echo form_input("eingabezeile", "eingabezeile");
echo form_close();

If I push the form button, the form fields are not available in the action-controller.
In my action-controller it allways says:
echo $_SERVER['REQUEST_METHOD']; --> "get".
And none of these work: $variable = $this->request->getPost("formfieldname"); doesnt give the value I entered.

I dont see the forest in front of the trees, as we say in german...

Thanks for a tip!
ME.