foo1.cs

var condition = expression.ConditionOperand;
if (condition == null) return;

var thenResult = expression.ThenResult;
if (thenResult == null) return;

var elseResult = expression.ElseResult;
if (elseResult == null) return;

// ...

foo2.cs

if (condition is {
     ConditionOperand is { } condition,
     ThenResult is { } thenResult,
     ElseResult is { } elseResult
   })
{
  // ...
}

foo3.cs

if (condition is ({ } condition, { } thenResult, { } elseResult))
{
  // ...
}