C# 8 understanding await using syntax

Similar as using (...) uses IDispose to clean up resources, await using (...) uses IAsyncDisposable. This allows to perform also time-consuming tasks (e.g involving I/O) on cleanup without blocking.

If SqlConnection implements IAsyncDisposable interface, Resharper suggests you to switch to await using to dispose it asynchronously using DisposeAsync method

public interface IAsyncDisposable
{
    ValueTask DisposeAsync();
}