main.js file structure.

import { createApp } from 'vue';
import App from './App.vue';
import router from './router';
import store from "./state/store";
import BootstrapVueNext from 'bootstrap-vue-next';
import i18n from './i18n';
import VueApexCharts from "vue3-apexcharts";
import { vMaska } from "maska";

import './assets/scss/app.scss';
import 'bootstrap-vue-next/dist/bootstrap-vue-next.css';
import 'simplebar/dist/simplebar.min.css';

createApp(App)
    .use(router)
    .use(store)
    .use(BootstrapVueNext)
    .use(i18n)
    .use(VueApexCharts)
    .directive("maska", vMaska)
    .mount('#app');

App.vue file structure.

<template>
    <router-view>
    
    </router-view>
</template>
  
<script>
  
export default {
    name: 'App',
    components: {
    }
};
</script>

You can set the default layout in the src/state/modules/layout.js file.