Sorry to inform you but the XSLT fiddle is currently offline, as it has reached its db quota limits.
In the browser you can continue to fiddle with SaxonJS XSLT 3 fiddle and my XSLT fiddle and the new CheerpJ 3, Saxon HE 12 Java powered XSLT 3.0, XQuery 3.1 and XPath 3.0 fiddle
If you are a Windows user you could try to install the .NET framework 4.8 WPF app XSLT, XQuery, XPath Notepad