Использовать System.Net.WebSockets.ValueWebSocketRece­iveResult в проекте Net Framework 4.8

System.Net.WebSockets.WebSocket client;
System.IO.MemoryStream stream = null;
buffer = buffer ?? ArrayPool<byte>.Shared.Rent(defaultReceiveBufferSize);
 
WebSocketReceiveResult receiveResult; // заменил ValueWebSocketReceiveResult
 
var receiveTask = client.ReceiveAsync(buffer.AsMemory(), token); // Error CS1503 Argument 1: cannot convert from System.ReadOnlyMemory<byte>' to 'System.ArraySegment<byte>'
if (receiveTask.IsCompleted)
     receiveResult = receiveTask.Result;
 
var writeTask = stream.WriteAsync(buffer.AsMemory(0, receiveResult.Count), token); // Error CS1501 No overload for method 'WriteAsync' takes 2 arguments
 
await stream.DisposeAsync(); // Error   CS1061 'MemoryStream' does not contain a definition for 'DisposeAsync' and no accessible extension method 'DisposeAsync' accepting a first argument of type 'MemoryStream' could be found (are you missing a using directive or an assembly reference?)

#if NET5_0_OR_GREATER
            ValueWebSocketReceiveResult receiveResult = await client.ReceiveAsync(buffer.AsMemory(), token);
            await stream.WriteAsync(buffer.AsMemory(0, receiveResult.Count), token);
            await stream.DisposeAsync();
#else
            WebSocketReceiveResult receiveResult = await client.ReceiveAsync(new(buffer), token);
            await stream.WriteAsync(buffer, 0, receiveResult.Count);
            stream.Dispose();
#endif

#if NETSTANDARD2_0
            WebSocketReceiveResult receiveResult = await client.ReceiveAsync(new(buffer), token);
            await stream.WriteAsync(buffer, 0, receiveResult.Count);
            stream.Dispose();
#else
            ValueWebSocketReceiveResult receiveResult = await client.ReceiveAsync(buffer.AsMemory(), token);
            await stream.WriteAsync(buffer.AsMemory(0, receiveResult.Count), token);
            await stream.DisposeAsync();
#endif

WebSocketReceiveResult receiveResult = await client.ReceiveAsync(new(buffer), token);

#if NETSTANDARD2_0
   private async Task SendInternalAsync(ArraySegment<byte> message)
#else
   private async Task SendInternalAsync(ReadOnlyMemory<byte> message)
#endif
{
 
}

        private void StartBackgroundThreadForSendingText()
        {
            messagesTextToSendQueue = Channel.CreateUnbounded<string>(
                new UnboundedChannelOptions
                {
                    SingleReader = true,
                    SingleWriter = false
                });
 
            _ = Task.Factory.StartNew(
                SendTextFromQueueAsync,
                cancellationTotal.Token,
                TaskCreationOptions.LongRunning,
                TaskScheduler.Default);
        }