Index: Classes/Builder/ContentTypeBuilder.php
IDEA additional info:
Subsystem: com.intellij.openapi.diff.impl.patch.CharsetEP
<+>UTF-8
===================================================================
diff --git a/Classes/Builder/ContentTypeBuilder.php b/Classes/Builder/ContentTypeBuilder.php
--- a/Classes/Builder/ContentTypeBuilder.php	(revision baf6013db728024501088c6b032aa315ce3c8a54)
+++ b/Classes/Builder/ContentTypeBuilder.php	(date 1729848771741)
@@ -249,7 +249,9 @@

     protected function addIcon(Form $form, string $contentType): string
     {
-        if (isset($GLOBALS['TCA']['tt_content']['ctrl']['typeicon_classes'][$contentType])) {
+        if (isset($GLOBALS['TCA']['tt_content']['ctrl']['typeicon_classes'][$contentType])
+            && preg_match('~^(?!content-)[^./]+$~', $GLOBALS['TCA']['tt_content']['ctrl']['typeicon_classes'][$contentType])
+        ) {
             return $GLOBALS['TCA']['tt_content']['ctrl']['typeicon_classes'][$contentType];
         }
         $icon = MiscellaneousUtility::getIconForTemplate($form);