Does anyone know what happened to the merge customers function (using one "display as" name)?

It seems to be working the same for me. When I edit a "Customer name" so it's the same as a different customer, I get a popup that asks "That name is already being used. Would you like to merge the two?"

Could you clarify which part isn't working for you?

Hi PatMcK, 

Welcome to the Community! QuickBooks Online offers a powerful platform that simplifies the way you handle your accounting. I can see the importance of being able to merge your customers and I'll be glad to assist. 

Here's how to merge customers in QB Online: 

1. Navigate to the Sales menu.
2. Click on the Customers tab.
3. Select and open the customer profile you don’t want to keep.
4. Hit Edit.
5. In the Display name as field, enter the name of the customer profile you want to keep. The names need to match exactly.
6. Click on Save.
7. When asked if you want to merge the two profiles, click Yes.

It's important to note that if your customers have sub-customers, those sub-customers will automatically turn into regular customers upon following the steps above. 

Let me know if this info helps, I'll be one message away in case you need additional support with this.