Issue #3466385 by just_like_good_vibes: Field formatter process text does not appear processed

src/Plugin/UiPatterns/PropType/SlotPropType.php

@@ -78,9 +78,7 @@ class SlotPropType extends PropTypePluginBase {
    */
   public static function convertFrom(string $prop_type, mixed $value): mixed {
     return match ($prop_type) {
-      'string' => [
-        '#plain_text' => $value,
-      ],
+      'string' => ($value instanceof MarkupInterface) ? ["#children" => $value] : ["#plain_text" => $value],
     };
   }