Drupal 8.x

Today I tried to configure a block and got the following:

Symfony\Component\Routing\Exception\MissingMandatoryParametersException: Some mandatory parameters are missing ("block") to generate a URL for route "entity.block.edit_form". in Drupal\Core\Routing\UrlGenerator->doGenerate() (line 182 of core/lib/Drupal/Core/Routing/UrlGenerator.php).

Always some new problems...

Context
we've build a decoupled drupal 8.x website on a Ubuntu 18.04 with apache as follows

backend
backend.domain.com
(a drupal 8.max install)
frontend
frontend.domain.com
(a next/react install)

vhost
frontend.domain.com proxies to the next app
the next app calls the drupal install via json (json api and custom endpoints)

in form alter I have to take the value of a date field
the code I use is this

$a = $form['field_data_rientro']['widget'][0]['value']['#value'];

but I don't get any results. I saw the array with Kint but the '#value' key is missing
How can I go about getting the value of the Date

Hi

I hope I'm not in the wrong part of the forum.

I simply cannot activate the Custom menu link translation under admin/config/regional/content-language.

I have activated other elements... See printscreen

I have a few modules, and maybe the one that could be a problem il Domain Access.

Any idea how to do it?

I have created a subtheme based on bootstrap 3 on Drupal 8. I do not want the bootstrap's table style show the file sizes. So, how do I remove it from there?

Note: I am not a tech-savvy person, therefore a detailed explanation would really be appreciated.

Thanks!