decode `IEnumerable` to string made of 1 byte characters (eg., ASCII)
Well, I could propose few improvements for you:

Try to use SelectMany instead of just Select;
No need to call ToArray since the string.Concat could consume IEnumerable;

public static string UintArrayToString(this IEnumerable&lt;uint&gt; x) =&gt;
    string.Concat(x.SelectMany(BitConverter.GetBytes).Select(Convert.ToChar));