foo1.cs

if (pattern is IPatternWithDesignation withDesignation)
{
  var existingDesignation = withDesignation.Designation;
  if (existingDesignation != null && !(existingDesignation is IDiscardDesignation)) return false;
}

foo2.cs

// after "Merge sequential patterns"

if (pattern is IPatternWithDesignation withDesignation)
{
  var existingDesignation = withDesignation.Designation;
  if (existingDesignation is { } and not IDiscardDesignation) return false;
}

foo3.cs

// after "Replace `and` with `or`"

if (pattern is IPatternWithDesignation withDesignation)
{
  var existingDesignation = withDesignation.Designation;
  if (existingDesignation is not (null or IDiscardDesignation)) return false;
}

foo4.cs

// inline variable, merge ifs, merge sequential patterns into recursive

if (pattern is IPatternWithDesignation { Designation: not (null or IDiscardDesignation) })
  return false;