Where to learn Twig for WordPress / {% set args %} - hierarchical CPTs

Hi guys,

I think that Twig is absolutely fantastic and I really want to learn it. However, I have great difficulty finding Twig code examples related to WordPress and Metabox, except for the basic stuff.
The documentation is quite limited.

1. You link to the official documentation of Twig on symfony.com, however in the context of WordPress it is not so useful. Basically, it's like a GRAMMAR of a language, but it lacks the specific "VOCABULARY" related to WordPress. Without the "vocabulary" used in the context of WordPress/Metabox, it's difficult for me to master it. Is there some more detailed reference with code examples, that I haven't been able to find?

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2. Is the implementation of Twig in Metabox compatible with Timber, so that their documentation can be applied to Metabox? I tried some things from there and they didn't work for me.

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3. At the moment, I would like to learn how to filter a loop query of CPTs.
   The CPTs are hierarchical and I would like to display all posts that have a parent post of the same type. For example, there is a CPT called "places" with such posts:

/japan/
/japan/tokyo
/japan/yokohama
/australia/
/australia/sydney

In the loop, I would like to display "Tokyo", "Yokohama", "Sydney" but NOT "Japan" and "Australia".
Also, I would like to show only posts which have a checkbox checked.

I suppose it is done through this:

{% set args = { post_type: 'places', posts_per_page: -1 } %}
{% set posts = mb.get_posts( args ) %}

I just cannot find out how to filter the query by the parent/child status and checkbox status...

I would not like to bother the support with basic questions, but it's not easy to find such answers about Twig in the documentation or elsewhere on the Internet. I have spent hours searching, but the online materials about Twig in relation to WordPress & Metabox are very scarce. It's quite difficult to find the required "vocabulary" for slightly more advanced tasks.

Greetings,
Tom