Popper.js problem with Bootstrap modals in Laravel 5.8 - bootstrap-modal

Question

I'm creating a web application based on Laravel 5.8 + Laravelmix + bootstrap + Vue
(which is how Lravel comes out of the box)
Problem is that bootstrap modals will not work - not out of the box at least.
If you try to trigger a modal you get an error in the console, regarding a popper map component (needed by jquery) that is there (in fact) but for some reason it doesn't get properly added to the mix.
This is a know problem: I found other questions and threads about this problem in Stackoverflow, however...
Problem in the problem: all existing QAs that i found take for granted that who reads knows quite a lot about npm webpack and laravel mix... and I don't! :-( I'm mostly a backend developer, not a frontend dev: I know basic Javascript but don't know much about webpack and I haven't been able to apply the suggested solutions to my case.
Could somebody explain to me in clear terms how my js assets should look like in order to work???
This is my webpack.mix file:
const mix = require('laravel-mix');
mix.js('resources/js/app.js', 'public/js')
.sass('resources/sass/app.scss', 'public/css');
This is my resources/js/app.js file:
require('./bootstrap');
window.Vue = require('vue');
Vue.component('example-component', require('./components/ExampleComponent.vue').default);
const app = new Vue({
el: '#app',
});
This is the beginning of my resoureces/js/bootstrap.js file looks like:
window._ = require('lodash');
try {
window.Popper = require('popper.js').default;
window.$ = window.jQuery = require('jquery');
require('bootstrap');
} catch (e) {}
window.axios = require('axios');
And finally this is my package.json file:
{
"private": true,
"scripts": {
"dev": "npm run development",
"development": "cross-env NODE_ENV=development node_modules/webpack/bin/webpack.js --progress --hide-modules --config=node_modules/laravel-mix/setup/webpack.config.js",
"watch": "npm run development -- --watch",
"watch-poll": "npm run watch -- --watch-poll",
"hot": "cross-env NODE_ENV=development node_modules/webpack-dev-server/bin/webpack-dev-server.js --inline --hot --config=node_modules/laravel-mix/setup/webpack.config.js",
"prod": "npm run production",
"production": "cross-env NODE_ENV=production node_modules/webpack/bin/webpack.js --no-progress --hide-modules --config=node_modules/laravel-mix/setup/webpack.config.js"
},
"devDependencies": {
"axios": "^0.18",
"bootstrap": "^4.0.0",
"cross-env": "^5.1",
"jquery": "^3.2",
"laravel-mix": "^4.0.7",
"lodash": "^4.17.5",
"popper.js": "^1.12",
"resolve-url-loader": "2.3.1",
"sass": "^1.20.1",
"sass-loader": "7.*",
"vue": "^2.5.17",
"vue-template-compiler": "^2.6.10"
}
}