C# LINQ - selecting a dynamic object based on properties defined at runtime

I've been trying to create an expression which can project a strongly typed EF Core entity into a dynamic object containing a list which are defined at runtime using a REST API call.

This is what I have so far:

Expression<Func<Message, dynamic>> DynamicFields(IEnumerable<string> fields)
{
    var xParameter = Expression.Parameter(typeof(Message), "o");
    var xNew = Expression.New(typeof(ExpandoObject));

    var bindings = fields.Select(o => {
        var mi = typeof(Message).GetProperty(o);
        var xOriginal = Expression.Property(xParameter, mi);
        return Expression.Bind(mi, xOriginal);
    });

    var xInit = Expression.MemberInit((dynamic)xNew, bindings);

    return Expression.Lambda<Func<Message, dynamic>>(xInit, xParameter);
}

It feels like I'm super close, but this bombs out at runtime stating that X property is not a member of ExpandoObject. I've tried changing up the use of the dynamic and ExpandoObject, but nothing seems to work - is this even possible?

If I switch out dyanmic / ExpandoObject for Message, it works just fine, but returns an instance of the Message class with all of its properties at their default values.

Anyone done this before?

Cheers.