This DEV-only field was added in 836331ba5f69f2cc53b273ec073fae116db14302 by @sebmarkbage but it's not being used anymore to my knowledge.
const innerPropTypes = type.propTypes;
      if (innerPropTypes) {
        
        
        checkPropTypes(
          innerPropTypes,
          nextProps, 
          'prop',
          getComponentNameFromType(type),
        );
      }
    }
    const child = createFiberFromTypeAndProps(
      Component.type,
      null,
      nextProps,
      workInProgress,
      workInProgress.mode,
      renderLanes,
    );
    child.ref = workInProgress.ref;
    child.return = workInProgress;
    workInProgress.child = child;
    return child;
  }
  if (__DEV__) {
    const type = Component.type;
    const innerPropTypes = type.propTypes;
    if (innerPropTypes) {