Drupal 8.x

On my Drupal 9 installation, I created a taxonomy vocabulary with terms and subterms.

I want to display under my nodes, a Views block with the other nodes that share the same parent terms.

I found this tutorial :

https://www.hashbangcode.com/article/drupal-9-using-taxonomy-terms-creat...

On my node types I created a field to select the taxonomy term (the category) :

Why I'm getting this error in Drupal 8? 

• Warning: Invalid argument supplied for foreach() in Drupal\Core\Extension\ThemeHandler->addTheme() (line 125 of core\lib\Drupal\Core\Extension\ThemeHandler.php).

Please give me some hint. 

I can't find the right hook to override the Entity Reference field settings on Edit Entity form, using Views Entity Reference, regarding to Views arguments, before the Views is executed for loading available items. Can anybody suggest me the right method?

As example on Default Drupal setup, on "Basic page" node I have the "Select list" entity reference to "Article" Node (which have "Tags" field), and have configured in it the Entity Reference Views that filter articles, with a single argument (Tags id = 1), like this:

Hi Guys, 

I'm trying to convert this drupal 7 theme() function in Drupal 8.

How can I achieve this thing ? 

Please help me I'm struggling with this. 

On yoursite/admin/config/content/formats (D 9.3.5) you define the order of your text formats and editors. In my case, it is like this:
1) php
2) plain text
3) basic html
etc.

So, when I add new text, the text format automatically selected is "php", no matter what content type. Yet, depending on the content type, it makes more sense to have a different text format on top. Is there a way to do this? For instance, the content type "biography" could have "basic html" on top, whereas the content type "code_snippet" could have text format PHP on top.

Hi guys,

I'm Converting Drupal 7 theme to Drupal 8 and in D7 I'm using my_theme_checkbox($variables) function for checkbox alteration but this function is not working in D8. 

Anyone please suggest me an alternative.