Hello varun31,
Thank you for using Apple Support Communities.
We understand that you upgraded your iPhone to iOS 14.1 and after doing so, YouTube will rotate just fine to the left. But when turning the phone to the right, the display will either not rotate or will rotate to the left. If this is only happening with YouTube, then take a lookout the following support article:
If an app unexpectedly quits, stops responding, or won’t open - Apple Support
If this is happening with other apps, then take a look at the following support article. Try turning off the option to turn screen rotation of and then back on.
Rotate the screen on your iPhone or iPod touch - Apple Support
Best regards.