Why is the browser showing blank content, depsite the front-end and and back-end running without any errors?

I am having an issue with my MERN-Stack application rendering blank content in the browser despite the front-end and back-end running without any errors.

In the browser, two errors are coming up through inspect;

1. Uncaught SyntaxError: Unexpected token '<' in main.b4d4fd26.js:1

2. Manifest: Line: 1, column: 1, Syntax error in manifest.json:1

What would be the solution to this?

Server:

const express = require("express");
const { ApolloServer } = require("apollo-server-express");
const path = require("path");
// require("dotenv").config();
require("dotenv").config({ path: path.resolve(__dirname, ".env") });

const { typeDefs, resolvers } = require("./schemas");
const { authMiddleware } = require("./utils/auth");
const db = require("./config/connection");

const PORT = process.env.PORT || 5000;
const app = express();

const server = new ApolloServer({
  typeDefs,
  resolvers,
  context: authMiddleware,
  // These two lines below enable the playground when deployed to heroku. You can remove them if you don't want this functionality
  introspection: true,
  playground: true,
});

server.applyMiddleware({ app });

app.use(express.urlencoded({ extended: false }));
app.use(express.json());

if (process.env.NODE_ENV === "production") {
  app.use(express.static(path.join(__dirname, "../client/build")));
}

app.get("*", (req, res) => {
  res.sendFile(path.join(__dirname, "../client/build/index.html"));
});

db.once("open", () => {
  app.listen(PORT, () => {
    console.log(`Server running on port http://localhost:${PORT}`);
    console.log(`Use GraphQL at http://localhost:${PORT}${server.graphqlPath}`);
  });
});

Manifest.json file:

{
  "short_name": "React App",
  "name": "Create React App Sample",
  "icons": [
    {
      "src": "favicon.ico",
      "sizes": "64x64 32x32 24x24 16x16",
      "type": "image/x-icon"
    },
    {
      "src": "logo192.png",
      "type": "image/png",
      "sizes": "192x192"
    },
    {
      "src": "logo512.png",
      "type": "image/png",
      "sizes": "512x512"
    }
  ],
  "start_url": ".",
  "display": "standalone",
  "theme_color": "#000000",
  "background_color": "#ffffff"
}