How to duplicate apps???

Presumably you are attempting to run multiple instances of the same App? If so, you need to explore iPadOS multitasking...

Key to accessing and controlling multi-tasking is the small “three-dot” button that is found at the top-centre edge of each App Window. Tap the multitasking button at the top of the slide-over window to expose a menu - from which you can change the window view and launch additional Apps in the same multi-window view.

More information about using multi-tasking can be found in this support page:

Use multitasking on your iPad - Apple Support

If your iPad supports Stage Manager, this provides additional multitasking capabilities:

Move, resize, and organize windows with Stage Manager on iPad – Apple Support

The iPad User Guide is also a rich source of information about using iPad and its many features. The Guide is available both online using a web browser (such as Safari):

iPad User Guide - Apple Support

You can't actually duplicate an app. You can create a shortcut that will open an App though, if that is what you are looking to do.