For iOS 14 you need iTunes 12.8.2.3 or better running on OS X 10.11.6 or better. See How to upgrade to OS X El Capitan - Apple Support if required.
Assuming a suitable version of iTunes is in place then in Finder use the menu item Go > Go to Folder..., copy the following text, paste it into the dialog box and press enter:
/System/Library/PrivateFrameworks/MobileDevice.framework/Versions/Current/Resources
Unlock your device and connect it to USB. Double click on MobileDeviceUpdater in the folder that has opened. It should notify you of a software update. Install it and iTunes should hopefully recognize your device.
If these steps haven't worked you can also try reinstalling iTunes 12.8.2.3 while your device is connected and unlocked. (Except you probably can't do that bit.)
See also If you can't update or restore your iPhone, iPad, or iPod touch - Apple Support.
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