//Get query parameter from POST vars:
//$field_date_value_ajax = \Drupal::request()->request->get('field_date_value'); // form param
//Incidentally, for GET vars, you would use:
$field_date_value_get = \Drupal::request()->query->get('field_date_value');
https://www.drupal.org/project/views_year_filter
You can alter form and set Exposed filter for year to be not text but select
//Get query parameter from POST vars:
//$field_date_value_ajax = \Drupal::request()->request->get('field_date_value'); // form param
//Incidentally, for GET vars, you would use:
$field_date_value_get = \Drupal::request()->query->get('field_date_value');
$form['field_date_value'] = [
'#type' => 'select',
'#options' => $options,
'#size' => NULL,
'#value' => $field_date_value_get ?: date('Y', time()),
];