@Suparth Ghimire Thanks for reaching here! It seems like there is an issue with the deployment of your Next.js app to Azure Static Web Apps. The error message you posted says that the page cannot be found.
Based on the GitHub Actions file you provided, the app_location is set to "/" and the output_location is set to ".next/standalone". This means that the source code for the app is located in the root directory of the repository and the built app content is located in the ".next/standalone" directory.
It is possible that the issue is with the app_location or output_location settings. You may want to double check that the source code and built app content are located in the correct directories.
You can also try to review the detailed logs of your workflow's run in GitHub Actions to see if there are any error messages or issues with the deployment.
If you are still having trouble, you may want to consult the Azure Static Web Apps documentation for more information on deploying Next.js apps.
Let us know.