list.Foreach((item) => {
    // You cannot break from here beacuse of the structure of the method.
      // Underneath is they way the meothd is tructured and a break is not allowed.
    //public static ForEach(this IEnumerable input, Action action)
    //{
      //foreach(var i in input)
    //    action(i);
    //}
});

// You have to convert your code into the traditional foreach:
foreach(var item in list) {
    // Your code here
      break; // <- As you can see you can break here.
}