Hi, after I update my iPad to 15.2.1 iPAD OS version. USB devices stops detecting. Please help.

If your iPad is misbehaving immediately after being updated, perform a forced-restart - as doing so will often resolve the issue:

• On an iPad with a Home button: Press and hold the top button and the Home button at the same time. When the Apple logo appears, release both buttons.
• On other iPad models: Press and quickly release the volume up button, press and quickly release the volume down button, then press and hold the top button. When the Apple logo appears, release the button.