Question

There are two formats for any given Linq expression with a custom sort comparer:

Format 1

var query =
    source
    .Select(x => new { x.someProperty, x.otherProperty } )
    .OrderBy(x => x, new myComparer());

Format 2

var query =
    from x in source
    orderby x // comparer expression goes here?
    select new { x.someProperty, x.otherProperty };

Question:
What is the syntax for the order-by expression in the second format?

Not the question:
How to use a custom comparer as shown in the first format.

Bonus credit:
Are there actual, formal names for the two Linq formats listed above?

Answer 1

What is the syntax for the order-by expression in the second format?

It doesn’t exist. From the orderby clause documentation:

You can also specify a custom comparer. However, it is only available by using method-based syntax.

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How to use a custom comparer in the first format.

You wrote it correctly. You can pass the IComparer<T> as you wrote.

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Are there actual, formal names for the two Linq formats listed above?

Format 1 is called “Method-Based Syntax” (from previous link), and Format 2 is “Query Expression Syntax” (from here).