using System;

using System.Linq;

using System.Collections.Generic;

public class Program

{

    public static void Main()

    {

        var list = new List<DateTime>()

        {

            new DateTime(2023, 05, 02),

            new DateTime(2023, 05, 03),

            new DateTime(2023, 05, 04),

            new DateTime(2023, 05, 10),

            new DateTime(2023, 05, 11),

            new DateTime(2023, 05, 20),

        };

        var results = list.GroupUp((a, b) => a.AddDays(1) >= b);

        results.Dump();

    }

}

​

public static class Extensions

{

    public static IEnumerable<IEnumerable<T>> GroupUp<T>(this List<T> source, Func<T, T, bool> isSameGroupFunc)

    {

        for (var start = 0; start < source.Count; start++)

        {

            var end = start;

            while (end + 1 < source.Count)

            {

                if (!isSameGroupFunc(source[end], source[end + 1]))

                    break;

​

                end++;

            }

            yield return SkipTake(source, start, end + 1);

            start = end;

        }

    }

    private static IEnumerable<T> SkipTake<T>(List<T> source, int start, int count)

    {

        for (var i = start; i < count; i++)

            yield return source[i];

    }

}