Hi,

What you can do for this is that, just override the create method the model hr.employee and assign the related user to the employee.

class HrEmployee(models.Model):    
    _inherit = 'hr.employee'  
 
    @api.model    
    def create(self, vals):               
        # In the vals you will have the work email and all other details        
        # compare the email with the mail of users        
        user_rec = self.env['res.users'].search([('login', '=', vals['work_email'])], limit=1)        
        vals['user_id'] = user_rec.id
        res = super(HrEmployee, self).create(vals)  
        return res

Just print the vals and see how to access the work email and user_id.  vals['work_email'] and  vals['user_id'], may not be the way to access it, just check and adjust accordingly

Thanks