See #17798
i
      const primaryChildFragment = fiber.child;
      const fallbackChildFragment = primaryChildFragment
        ? primaryChildFragment.sibling
        : null;
      const fallbackChild = fallbackChildFragment
        ? fallbackChildFragment.child
        : null;
      if (fallbackChild !== null) {
        mountFiberRecursively(
          fallbackChild,
          shouldIncludeInTree ? fiber : parentFiber,
          true,
          traceNearestHostComponentUpdate,
        );
      }
    } else {
      if (fiber.child !== null) {
        mountFiberRecursively(
          fiber.child,
          shouldIncludeInTree ? fiber : parentFiber,
          true,
          traceNearestHostComponentUpdate,
        );
      }
    }
     W
     I
    updateTrackedPathStateAfterMount(mightSiblingsBeOnTrackedPath);
    if (traverseSiblings && fiber.sibling !== null) {