[Vuejs]-Vue is not defined/not a constructor

It looks like your initialization code is for Vue 2:

import Vue from 'vue'

let featured = new Vue({
    el: '.featured--vue_js',
    /*...*/
})

But your project has Vue 3 installed, so you should be using Vue 3’s createApp():

import { createApp } from 'vue'

let featured = createApp({
    /*...*/
}).mount('.featured--vue_js')