diff -u b/core/lib/Drupal/Core/Datetime/Element/Datetime.php b/core/lib/Drupal/Core/Datetime/Element/Datetime.php
--- b/core/lib/Drupal/Core/Datetime/Element/Datetime.php
+++ b/core/lib/Drupal/Core/Datetime/Element/Datetime.php
@@ -377,4 +377,27 @@
 
   /**
+   * Creates an example for a date format.
+   *
+   * This is centralized for a consistent method of creating these examples.
+   *
+   * @param string $format
+   *   The date format.
+   *
+   * @return string
+   *
+   * @deprecated in drupal:10.1.0 and is removed from drupal:11.0.0. HTML date
+   *   input format should not be exposed to users, as browser widgets expose
+   *   input differently, varying by vendor, locale, device type, etc.
+   * @see https://www.drupal.org/project/drupal/issues/2791693
+   */
+  public static function formatExample($format) {
+    @trigger_error(__METHOD__ . ' is deprecated in drupal:10.1.0 and is removed from drupal:11.0.0. No replacement provided. https://www.drupal.org/project/drupal/issues/2791693', E_USER_DEPRECATED);
+    if (!static::$dateExample) {
+      static::$dateExample = new DrupalDateTime();
+    }
+    return static::$dateExample->format($format);
+  }
+
+  /**
    * Retrieves the right format for an HTML5 date element.
    *