Gulp build for IE11

A website was created using gulp. The trouble is that in IE, the scripts do not work, although it seems that everything you need is configured. The build was done by the lead programmer, but he can't help now, unfortunately. I didn't work with GULP myself, so I thank you in advance for your help.

Here are the file codes

Package.json

{
  "name": "marker",
  "version": "1.0.0",
  "main": "gulpfile.js",
  "scripts": {
    "start": "node gulpfile.js"
  },
  "author": "strangebrain",
  "license": "ISC",
  "devDependencies": {
    "@babel/core": "^7.9.6",
    "@babel/plugin-transform-classes": "^7.12.1",
    "@babel/preset-env": "^7.9.6",
    "@rollup/plugin-babel": "^5.0.0",
    "@rollup/plugin-commonjs": "11.0.2",
    "@rollup/plugin-node-resolve": "^7.1.3",
    "browser-sync": "^2.26.7",
    "flickity": "^2.2.1",
    "flickity-fade": "^1.0.0",
    "gulp": "^4.0.2",
    "gulp-autoprefixer": "^7.0.1",
    "gulp-babel": "^8.0.0",
    "gulp-better-rollup": "^4.0.1",
    "gulp-cssnano": "^2.1.3",
    "gulp-plumber": "^1.2.1",
    "gulp-postcss": "^8.0.0",
    "gulp-sass": "^4.0.2",
    "gulp-uglify-es": "^2.0.0",
    "rellax": "^1.12.1",
    "rollup": "^1.32.1"
  },
  "dependencies": {
    "appear": "^1.0.1",
    "appear-js": "^1.0.2",
    "chartist": "^0.11.4",
    "rollup-plugin-import-css": "^1.1.2"
  },
  "description": "marker",
  "browserslist": [
    "> 1%",
    "IE 11"
  ]
}

Gulpfile.js

let gulp = require("gulp");

//CSS PLUGINS
var scss = require("gulp-sass");
var autoprefixer = require('autoprefixer');
var cssnano = require('cssnano');
var postcss = require('gulp-postcss');

//JS
var babel = require('gulp-babel');
var uglify = require('gulp-uglify-es').default;
var rollup = require('gulp-better-rollup');

// Add support for require() syntax
var commonjs = require('@rollup/plugin-commonjs');
var resolve = require('@rollup/plugin-node-resolve');

//Browser Sync
var browserSync = require("browser-sync");

//Output
var themePath = './'
var sassFile = themePath + 'sass/**/*.scss';
var jsFile = themePath + 'js/**/*.js';

//TASKS
gulp.task('compileCSS', function() {
    var plugins = [
        autoprefixer(),
        cssnano()
    ];

    return gulp.src(sassFile)
        .pipe(scss())
        .pipe(postcss(plugins))
        .pipe(gulp.dest(themePath + 'build'))
        .pipe(browserSync.stream())
});

gulp.task('compileJS', function() {
    var plugins = [
        commonjs({include: /node_modules/}),
        resolve(),
        babel({presets: ['@babel/env']}),
    ];

    return gulp.src(jsFile)
        .pipe(rollup({plugins: plugins}, { format: 'iife' }))
        .pipe(uglify())
        .pipe(gulp.dest(themePath + 'build'))
        .pipe(browserSync.stream())
})

gulp.task("watch", function(done) {
    browserSync.init({
        proxy: 'http://exter.ru/OutSource/wp.marker2020.loc/',
    })

    gulp.watch(sassFile, gulp.series('compileCSS'));
    gulp.watch(jsFile, gulp.series('compileJS'));
    gulp.watch([
        themePath + '**/*.php'
    ]).on('change', browserSync.reload);
});

gulp.task('default', gulp.series('compileCSS', 'compileJS', 'watch'));