Parse time error Fatal error: Uncaught DateMalformedStringException:

I’m studying the date function in PHP and ran into the same problem. An error occurs in my code that works with a large date. Help me understand what the problem is with this code.

   $start = new DateTime('02.12.20239');
   var_dump($start);

This code throws an error:
Fatal error: Uncaught DateMalformedStringException: Failed to parse time string (02.12.20239) at position 10 (9): Unexpected character in C:ProjectsPhptest1test1.php:2
How to work with large dates in php?