[Vuejs]-Vue Application : Footer doesn't render and give my 2 errors and warning

You are calling the Footer component inside the Footer component:

src/components/Footer.vue

<template>
  <Footer>
...

use the built-in HTML <footer> element instead (lower case f)

As @tauzN points, you’re creating an infinite loop by calling the component Footer inside Footer.

You should use a multi-word name approach for your components:

This prevents conflicts with existing and future HTML elements, since all HTML elements are a single word.

You can read more at https://v2.vuejs.org/v2/style-guide/#Multi-word-component-names-essential