why i am not able to connect my iphone to computer

Connect iPhone to Computer / Mac

Settings > Touch/Face ID & Passcode > USB Accessories > [Enable]

You haven't mentioned whether you have a PC or Mac. However...

1. Use your USB lightening cable --> Resolve USB-related alerts in iTunes - Apple Support
2. If unable to connect --> If iTunes doesn't recognize your iPhone, iPad, or iPod - Apple Support
3. If your computer is a...
   1. Mac --> If your computer doesn't recognize your iPhone, iPad, or iPod ...
   2. Windows PC —> Troubleshooting issues with iTunes for Windows - Apple Community
4. Use genuine cable --> Identify counterfeit or uncertified Lightning connector accessories ...
5. See how to --> Sync your iPhone, iPad, or iPod using iTunes on your computer ...

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