Hi,

What you have to do is that, just inherit the model mail.wizard.invite and set the default=False in the code.

class Invite(models.TransientModel):
    _inherit = 'mail.wizard.invite'

    send_mail = fields.Boolean('Send Email', default=False,
                               help="If checked, the partners will receive an email warning they "
                                    "have been added in the document's followers.")

To set default value for a field from the UI by activating the developer mode, have a look at this video: How To Set Default Value For A Field in Odoo

Thanks