How add an autocomplete field in a class who extends FormBase ?

I created a custom module, in the custom module there is a "Form" file (a class who extends FormBase) In the form file, I want create programmaticaly a form element like a entity reference field (an autocomplete users list of the site)

How can I do that ? I search in the core, in the web...but I don't find how do that

How do I add an autocomplete field in a class that extends FormBase?

I created a custom module, which uses a class that extends FormBase. I want to programmatically create a form field that autocompletes the username from the user registered in the site.