Drupal

Create Drupal 8 Custom Page Template

Simply place the following code in the .theme (theme_name.theme) file that is located inside your theme folder. Replace theme_name with the actual name of your Drupal theme.

function theme_name_theme_suggestions_page_alter(array &$suggestions, array $variables) {
// Add content type suggestions.
if ($node = \Drupal::request()->attributes->get('node')) {
array_splice($suggestions, 1, 0, 'page__' . $node->getType());
}
}

Then create a file under the template folder and name it according to your node content type e.g.

page--page.html.twig

Then add your custom code for that particular page.