8 How to set a value for select list, While using $entity->set('field_name_type_select_list', ["Se_the_optional_value"]); Programmatically?
You can use hook_ENTITY_TYPE_presave as in hook_ENTITY_TYPE_update

When saving existing entities, the entity is assumed to be complete, partial updates of entities are not supported.

use Drupal\node\NodeInterface;

function mymodule_node_presave(NodeInterface $node) {

  switch ($node-&gt;getType()) {
    case "article":

      $node-&gt;set('field_set_color', ["red","green"]);

      break;

  }

}