Allow me to share some information about duplicating estimates in the new QuickBooks experience.
QuickBooks has been gradually introducing its updated layout to users since 2023. While the new layout offers many enhancements, there are still features from the old one that aren't available. This includes the ability to duplicate an estimate. Thus, I suggest sending feedback. Doing so helps our product engineers know the feature you need and may add it in future updates. I'll guide you on how to send your comments and suggestions.