How do I get block relationships for a content type? As part of a migration from drupal 7 to drupal 8, I currently have a rather original node display method that I'm trying to reproduce to Drupal 8, but without success.
Currently on Drupal 7, this method is filled by a custom preprocess that I try to remove in favor of views / entity reference.

Here is the procedure:
I have a node type that contains tags (field_tags), with for example the vocabulary 'news' from the 'Users terms' term. And basic content (title, body...).
I would like, via an already existing block having a field tags and value 'news', recover all the nodes with the tag 'news'.

Recap of entities I have tried:

Node:
- title
- body
- field_tags / value: 'news' (reference to "User terms")

Views name 'flow': 
- display: content
- contextual filter: 'Content: Has taxonomy term ID' > 'Display all results for the specified field'
&amp; Content: Nid
- relationsips: nothing, because I can't add a entity reference to a block

Block name 'block flow' :
- title
- field_tags / value: 'news' (reference to "User terms")

I would like when I create a block type 'block flow' with 'news' tags, get all node type that containing the 'news' tag.

I can't get it working because the views relationships don't allow me to reference the field 'field_tags' from my block (only content or taxonomy available).
We have a theme preprocess who can do that but I would like to know if there is a workaround ou any contrib module doing that.

Why I don't create a block from the view? Because in our process, we don't give access to the views of our contributors.
Finally, I got this working by creating a simple view "custom block".
Then, I created 3 relations, one for my node content, one for my content tags and last one for block tags

After that, we just need a contextual filter : Content: Has taxonomy term ID' > 'Display all results for the specified field

And that's all.