Can’t download new App on IPhone X... a wired sceeen appears asking to double click ... nothing happens.

If you are referring to the iPhone X as well, since that is what this thread is about, that is the method for downloading an app from the App Store, especially if you have activated Face ID for the App Store. You double-tap the side button on the phone to activate the Face ID to recognize you and approve the purchase. See this support document, the section on "Use Face ID to make purchases."

In the iTunes Store, App Store, and iBooks Store

To use Face ID to purchase content from the iTunes Store, App Store, and iBooks Store, go to Settings > Face ID & Passcode and make sure that iTunes & App Store is turned on. Then follow these steps:

1. Open the iTunes Store, App Store, or iBooks Store, then tap something that you want to buy.
2. When prompted to pay, double-click the side button, then glance at your iPhone X.
3. Wait for Done and a checkmark to display.

You might be asked to enter your Apple ID password for the first purchase you make in the iTunes Store, App Store, or iBooks Store.

You don't tap the screen, you double-click the physical side button.

Do as the screen says and double-click the physical side button on the right side of your iPhone.

What is so bizarre is that Apple is usually so informative. The double click was very hard to figure out. I had to come to AppleCare to help. Very unApple. Not happy at all with the X. Shoulda kept up the old style.

Could you post a screenshot of that screen?

just so you know you can only get apps from app store you can't get apps from various web pages

How can I download app instead of getting some wired screen that appears on my phone to double click