you have not exported your Navbar component from Navbar.js file. please ask the question with more information, provide code for each file.

if you have exported using default

export default Navbar

you will import like this

import Navbar from "./Navbar.js"

if you have exported without default

import {Navbar} from "./Navbar.js"

for this you export like "export const Navbar" or in case of class "export class Navbar"