I was wondering that apart from creating wordpress themes, we can also create wordpress plugins with Pinegrow.
I maybe talking out of turn, I do not own the wordpress version of PG.
Pinegrow is not a development tool, it was designed for one thing and that is to create the visual mockup and layout of web pages.
If I were to develop for Wordpress I would setup a stand alone testing environment with PHP and MySQL installed and use Atom and Chrome web browser to write and test. Though you can also use something like Jetbrains IDE PhpStorm or MS Visual Studio Code.
I personally would not use PG to do any sort of backend coding especially with a complex CMS like Wordpress. The frontend pretty absolutely but the backend development, no I would not.
Can it be done? There is a text editor, you can write and edit code, so technically it could be achieved. You are not going to get any troubleshooting though, no variable checking or context sensitive code insertion / replacement and definitely no code trapping or looping.
Pinegrow is not setup to be a developers tool for that type of thing, could you use it to write wordpress plugins? I would rather use Notepad++ or a straight text editor than PG to do it but YOU could do it with PG I suppose. Just be aware of the headaches and disadvantages you will put yourself under.