using static System.Console;

using static System.Convert;

using System.Text;

WriteLine(WrapString("0123456789012345678901234567890123456789", 10));

WriteLine(WrapString("01234567890123456", 10));

WriteLine(WrapString("012345", 10));

​

static string WrapString(string text, int len) {

    if (text.Length <= len) return text;

    StringBuilder sb = new(text.Length + text.Length / len * 2);

    var i = 0;

    for (; i < text.Length / 10; i++) {

        sb.Append(text[(i * 10)..(i * 10 + 10)]);

        sb.Append("\r\n");

    }

    if (text.Length / 10 != ToSingle(text.Length) / 10) {

        sb.Append(text[(i * 10)..]);

        sb.Append("\r\n");

    } else sb.Remove(sb.Length - 2, 2);

    return sb.ToString();

}