How to embed views in a particular custom block template
Ok, I have found a way to do so from another post, tested and it works ! So basically..

1) Create a new variable in mytheme.theme file located in your default theme folder.

function mytheme_preprocess_block(&amp;$variables) {

  $variables['view1'] = views_embed_view('view_name', 'block_news');

}


'block_news' is your views block's machine name actually. 

2) And then use this twig in your block template.

 {{ view1 }}