How to add custom menu items and shapes in context menu of Desktop version

I would like to get an example of a plugin that adds new elements. I need a plugin for the Desktop version of Camunda Modeler.
Ideally, I would like to get the following output:

image

How can I use it? May I upload this dir to my plugin?

Please read the example readme. If you want to create a Camunda Modeler extension, you may also need to look into this: https://github.com/camunda/camunda-modeler-plugins/tree/master/bpmn-js-plugin-example

I trying to add a plugin but nothing comes out. I can’t add service task to the pallete.

You can use this example of a Camunda Modeler plugin to create your own plugin: https://github.com/camunda/camunda-modeler-plugins/tree/master/bpmn-js-plugin-example

Conceptually, every bpmn-js plugin can be a Camunda Modeler plugin. A Camunda Modeler plugin simply takes a bpmn-js plugin and makes it available in the Camunda Modeler.