EnsureCapacity should not have if (newCapacity < min) newCapacity = min;

[viveknuna]

I think if (newCapacity < min) newCapacity = min; should be removed, I have added items to the full capacity of the list but never hit breakpoint on line newCapacity = min;, Can someone tell the purpose of this line as well?

        private void EnsureCapacity(int min) {
            if (_items.Length < min) {
                int newCapacity = _items.Length == 0? _defaultCapacity : _items.Length * 2;
                // Allow the list to grow to maximum possible capacity (~2G elements) before encountering overflow.
                // Note that this check works even when _items.Length overflowed thanks to the (uint) cast
                if ((uint)newCapacity > Array.MaxArrayLength) newCapacity = Array.MaxArrayLength;
                if (newCapacity < min) newCapacity = min;
                Capacity = newCapacity;
            }
        }

[svick]

Without that line, the array would grow, but it would not honor min. For example, if you have a list with Capacity = Length = 4 and AddRange a collection with 6 items, removing that line would grow the list to 8, when it needs to grow to 10.

Note that the equivalent .Net 7 source contains a comment explaining this.