Why does the custom app and document examples not use the new SGG methods?

[Axedyson]

So in your custom app and document examples, the getInitialProps method is used. But the two new methods (getStaticProps and getServerSideProps) is preferred instead of getIntialProps when using next js version 9.3 or newer. So what is the "new right" way to implement server-side data fetching in the custom document and app component using next js 9.3?