Get a list of all fields in Drupal 9/10

example.php

<?php

    // Get all Node types and all fields
    $content_types = NodeType::loadMultiple();
    foreach ($content_types as $content_type) {
      $types_options[$content_type->id()] = $content_type->label();
      foreach (\Drupal::service('entity_field.manager')->getFieldDefinitions('node', $content_type->id()) as $field_name => $field_definition) {
        if (!empty($field_definition->getTargetBundle())) {
          $field_options[$field_definition->getName() . ':' . $field_name] = $field_definition->getLabel();
          //display content type names in the drop down
          //$field_options[(string) $content_type->label()][$field_definition->getName() . ':' . $field_name] = $field_definition->getLabel();
        }
      }
    }
  
    asort($field_options);