Drupal - Check if a config entity type is a content entity type (or fieldable entity type...etc)

config_entity_type_is_a.php

<?php

use Drupal\Core\Entity\ContentEntityInterface;
use Drupal\Core\Entity\FieldableEntityInterface;

$entity_types = \Drupal::service('entity_type.manager')->getDefinitions();

/** @var \Drupal\Core\Config\Entity\ConfigEntityInterface $entity_type */
foreach ($entity_types as $entity_type) {
  // Stop now if entity type is not fieldable.  
  if (!$entity_type->entityClassImplements(FieldableEntityInterface::class)) {
    continue;    
  } 
  
  // Stop now if entity type is not a cnntent entity type.
  if (!$entity_type->entityClassImplements(ContentEntityInterface::class)) {
    continue;
  } 

  // Do your things now...
}