I can see the importance of item descriptions for you, @Repairs2day. 

Recently, QuickBooks Online updated its estimates and invoice layout to a newer one. This explains why the description of items isn't showing up on the drop-down menu like it used to.

No worries, because the description of items will continue to show up on the Description column once you've clicked the specific item you want to add. You can continue doing the steps on how to create an invoice. 

You can also check this article to see what’s new with estimates and invoices in QuickBooks Online.

Don't hesitate to reply below for more questions. The Community is happy to help. Enjoy the rest of the day, keep safe.