First, let's check to make sure your CircuitPython & Apple devices are ready to talk to eachother.
At the time of this writing iOS & iPadOS have been tested and confirmed to work with CircuitPython version 4.1.0.
Connect your CircuitPython compatible device to your computer (not the iOS device), and open the boot_out.txt file and check what version of CircuitPython you're running.
If you don't see a file named boot_out.txt or you have an older (than 4.1.0) or alpha version of CircuitPython installed, update to the latest stable release using these instructions.
On your iPhone/iPad, check what version OS you're running by opening the Settings app and tapping General->About and checking the Software Version number.
If your version number is 13 or later, you’re good to go. If not, update your OS via Settings->General->Software Update.
For devices with a Lightning connector – connect your Lightning to USB Adapter to iPhone/iPad and connect your CircuitPython device to the adapter via a micro USB cable.
For devices with a USB-C connector – connect your CircuitPython device directly to your iPad using a USB-C to Micro-B cable.