I use TinyMce 5 version with vue.js 2. I have like this options in my case:

editorOptions: {
  height: this.height,
  menubar: false,
  forced_root_block : false,
  plugins: [
      'advlist lists image charmap print preview anchor',
      'searchreplace visualblocks code fullscreen',
      'insertdatetime link table paste code help wordcount stylebuttons'
  ],
  color_map: [
    "32D7A0", "Green",
    "B4BDC4", "Gray",
    "FFFFFF", "White",
  ],
  custom_colors: false,
  language: 'ru',
  toolbar_sticky: true,
  autosave_ask_before_unload: true,
  content_style: '.text-green { color: #32D7A0; } ' +
  '.text-white { color: #ffffff; } ' +
  '.center { text-align: center; } ',
  toolbar: this.toolbar,
  setup: function (edt) {
    window.tinymce.PluginManager.add('stylebuttons', function(editor) {
        ['pre', 'p', 'code', 'h1', 'h2', 'h3', 'h4', 'h5', 'h6'].forEach(function(name){
            editor.ui.registry.addButton("style-" + name, {
                tooltip: "Toggle " + name,
                text: name.toUpperCase(),
                onClick: function() { editor.execCommand('mceToggleFormat', false, name); },
                onPostRender: function() {
                    var self = this, setup = function() {
                        editor.formatter.formatChanged(name, function(state) {
                            self.active(state);
                        });
                    };
                    editor.formatter ? setup() : editor.on('init', setup);
                }
            })
        });
    });
  }, 
}

Here I tried register stylebuttons plugin which add some buttons. But currently added buttons not shows in toolbar. How I can correctly add buttons in plugin?