As we discussed @MariemAbdi, UI/UX is a big pilar of front-end development. Your website, although fully functional, could benefit a lot from a refactoring of the User Interface. Ergonomic websites could help us look more professional and friendly and get more customers easily.
Here are a few things that you could start with:

• Use another font Take a look at Google fonts
• Remove the scroll bar when you don't need to scroll
• Update the colors that are in use. You need one primary color (the orange from your logo) and one secondary color (gray would look good I guess)
• Refactor the products table to a products grid catalog. Like in this website
• Refactor the product details page to a 2 column display like in this website
• For the general look of the pages Login and Signup, remove the navbar, put your logo at the top of the form and create a form like this one. The gray container does not look good

In your current code, any user of the platform can directly call any API with his Bearer Token and do things he is not supposed to do. For example, normal clients can create, delete, and update products.
To solve this, you should implement an authorization middleware in your Express app.
The middleware is just a function that you can pass to the route before the request handler and it should:

1. Get the Bearer Token from the request
2. Check if the user exists. Otherwise, return an error response.
3. Check if the user role is admin. Return an error response in case the user is not an admin.
   In the end, you'll have to add a role attribute to your users. And create a function like this:

const authorize = (role) => (req, res, next) => {
  // calls next() if user has required role
  // returns error response if the user does not have the required role
}

And then call it this way

router.post("/products", authorize("admin"), createProduct)

In the API calls from the frontend, you'll have to make sure you send the Bearer Tokens in the requests.

Resources

For more on Express middlewares, take a look at this article.