+1 to this request. Now that we have USB-C, this would make a big difference in enabling addiitonal Pro experiences on iOS, for example to connect to networking, radio or other control-over-serial equipment.
I have seen this exists: https://redpark.com/usb-c-serial-cable/ but is limited to using the Redpark Serial SDK and to Apps deployed via Apple Business Manager and Apple School Manager. To me, it seems it would help the wider ecosystem to enable serial support overall and consistently between iPhones and iPads.