Drupal 8.x

I added a new content type naming 'Custom Page'. I want to create a new template for all of the content with the content type 'Custom Page'.

I added the below code into my custom.theme file:

function yan_theme_suggestions_page_alter(array &$suggestions, array $variables) {
  if ($node = \Drupal::routeMatch()->getParameter('node')) {
    $suggestions[] = 'page__' . $node->bundle();
}

I understand that it needs to create a file xxx.html.twig in theme/custom/templates, right?

After an update I get an 500er error:

[01-Sep-2021 15:42:20 Europe/Berlin] PHP Fatal error:  Uncaught Error: Class 'ComposerAutoloaderInitDrupal8' not found in /homepages/16/d123456789/htdocs/drupal8/vendor/autoload.php:7
Stack trace:
#0 /homepages/16/d123456789/htdocs/drupal8/autoload.php(16): require()
#1 /homepages/16/d123456789/htdocs/drupal8/update.php(14): require_once('/homepages/16/d...')
#2 {main}
  thrown in /homepages/16/d154844430/htdocs/drupal8/vendor/autoload.php on line 7

Does anybody know what the problem is?

Hello,

I have created a link field and in the database we have tables for it as node__field_link and node_revision__field_link  . I am able to added contents programmatically but there is a field field_link_options with the type BLOB which is supposed to be binary, but opening it in text editor we I see only a:0:{}. 

my questions: 

1-How can I add that a:0:{} into this field? will simple insert of a:0:{} as string work?

Environment : Drupal 8.8.6 on Cloud

Scenario:

I have configured OIDC for SSO using company provided facilities to do so. (clientid, redirect uri, authorization endpoint-we get this from our corporate tool and configure this in custom jquery/js file)