Extend Order Model for use in email templates not longer working

i have a plugin for adding an order function to the order model. This worked before, but now it is no longer working. Maybe a problem with update to 2.3.3 or 2.3.4.

module.xml

< ?xml version="1.0"?>


    
        
    

di.xml

Model/Sales/Order.php

namespace MymoduleFormalsalutationModelSales;

class Order extends MagentoSalesModelOrder {

    public function getCustomerNameFormal() {
        $customerNameFormal = 'test';

        // removed logic here

        return $customerNameFormal;
    }
}

Email template usage (order and invoice template):

{{var order.getCustomerNameFormal()}}

When i open an order, it loads this model. But in the emails it is no longer working.
Has anyone an idea why this happens, was there a change in an update or is this just a bug?

I saw that other variables not working, too.

 {{var order.getCreatedAtFormated('long')}}

That is from the “insert variable” function, nut t is empty in email. But some, like address and Order ID are working.

Thank you,
Andreas