It doesn't appear that your engineers are doing anything. The feature disappeared out of the old experience about 6 months ago.. Even my basic xero accounting subscription includes a view and accept estimate link in their emails. 

As much as I appreciate your input your suggestion to manually send an invoice is unacceptable. It's 2023 not 1996 and customers expect to view estimates and accept them online. 

In addition how do you roll this feature out to some people and not others? Do I pay less for my QuickBooks advanced as it doesn't have the most basic functionality of an online estimate?