martini4ka

Так пробуйте с Gulp4:

const
  gulp          = require('gulp'),
  sass          = require('gulp-sass'),
  sourcemaps    = require('gulp-sourcemaps');
  browsersync   = require("browser-sync").create(),


function gulpSass() {
  return gulp
    .src('./scss/**/*.scss')
    .pipe(sourcemaps.init())
    .pipe(sass().on('error', sass.logError))
    .pipe(sourcemaps.write('./'))
    .pipe(gulp.dest('./css'))
    .pipe(browsersync.stream())
}


function browserSync(done) {
  browsersync.init({
    injectChanges: true,
    server: {
      baseDir: "./"
    },
    port: 3000,
    notify: false
  });
  done();
}


function watchFiles(done) {
  gulp.watch('./scss/**/*.scss', gulp.parallel(gulpSass));
  done();
}

const watch = gulp.parallel(watchFiles, browserSync);


exports.watch = watch;

function reload(done) {
  browsersync.reload();
  done();
}

Только установите browsersync , без него ничего не получится)