Why does symfony twig throw an error when accessing a controller?

Question

symfony

I'm starting to study symphony, I installed it through the website composer. created a controller, launched the built-in web server and gives an error

(4/4) Twig_Error_Syntax

An exception has been thrown during the compilation of a template ("Warning: mb_substr_count(): Unknown encoding "0"") in "@Twig/Exception/exception_full.html.twig".

php 7.2 openserver

Answer 1

Edit this file
@Twig/Exception/exception_full.html.twig (I think this path is in vendor/twig/... but check the help) or just clear it.
But this is a small part of the problem. It would be nice if you wrote how you built the local project, what version of cmf