Why does red minus symbol does not appear on my iPhone x even after i have press and hold the screen?

Yes, the red minus symbol in the app switcher has been removed intentionally by Apple in iOS 12. Most users (myself included) seem to agree that closing an app is now easier and much quicker...just swipe it up. I´m sure you'll get used to it...!

I assume you're talking about closing an app while in the app switcher, and that you're running iOS 12!? This has changed in iOS 12, you no longer need to press on an app and wait for the red minus symbol to appear...you just swipe the app up and away. Look at this article from Apple:

How to force an app to close on your iPhone, iPad, or iPod touch - Apple Support

Hope this helps you! Regards, Ian.

You're very welcome! Glad to have helped 🙂!

So happy they made this change back to the better way it used to work. Occasionally, Apple recognizes and rectifies their errors.

Yes, I couldn't agree more...!!