In Next.js, you can achieve such redirects by using the useRouter hook provided by next/router. Here's how you can redirect from the start page / to /hello-nextjs based on a condition:
1. First, ensure you have next/router installed in your Next.js project. If not, you can install it using npm or yarn:
npm install next/router
or
yarn add next/router
2. In your component, you can use the useRouter hook to get the current route information and perform a redirect if the condition matches:
import { useRouter } from 'next/router';
   const HomePage = () => {
     const router = useRouter();
     // Check if the path is '/'
     if(router.asPath === '/') {
       // Redirect to '/hello-nextjs'
       router.push('/hello-nextjs');
     }
     return (
       <div>
         {/* Your homepage content */}
       </div>
     );
   };
   export default HomePage;
3. Make sure to update the HomePage component with your actual content and structure.
4. When a user accesses the root path /, the HomePage component will check the route using useRouter and if it matches /, it will redirect the user to /hello-nextjs.
This way, you can achieve conditional redirects in Next.js similar to how you would do it in react-router.