Is it possible to filter the test cases whether it has been executed or not?

You're right.  It's obviously needed but it doesn't exist.  You can sort by the Last Test Execution (grey/green/red) icons to see which ones haven't been executed (greys), or, you could run a report like test execution results (list) > export the data to Excel > and from there run some analysis.  It's not perfect but both of those I think will help you work around the issue but let me know if not?