How can evaluate expression in Immediate window

Example Code:
class VisualizerComponent : IDkmCustomVisualizer{
IDkmCustomVisualizer.EvaluateVisualizedExpression(DkmVisualizedExpression visualizedExpression){
using (var LanguageExpression = DkmLanguageExpression.Create(
ParentInspectionContext.Language,
DkmEvaluationFlags.DesignTime | DkmEvaluationFlags.TreatAsExpression,
$"sizeof({rootExpr.FullName})",
null
))
{
//Evaluate it
}
}
}
but evaluate this failed.
but evaluate "sizeof" work in immediate window,what should i do

Start at VisualizerComponent.IDkmCustomVisualizer.EvaluateVisualizedExpression and the DkmLanguageExpression.Create call shown in the issue. Compare how the same sizeof expression is evaluated in the Immediate window; done means identifying why this evaluation fails and documenting or validating a working evaluation path.