1. Define your form view with the specific fields that you want to show.

2. Then return a form view in your model, like this:

@api.model
def my_action(self):
    try:
        form_view_id = self.env.ref("my_module.my_form_view_external_id").id
    except Exception as e:
        form_view_id = False
    return {
        'type': 'ir.actions.act_window',
        'name': 'My Action Name',
        'view_type': 'form',
        'view_mode': 'form',
        'res_model': 'my.model',
        'views': [(form_view_id, 'form')],
        'target': 'current',
    }