iPad can't connect to iMac via cable

I have a Retina 5K, 27 inch, late 2014 iMac running OS 11.7.10 and a 1st generation 11 inch iPad Pro from 2018 running iPadOS 17.2.

Two connect the two, I used a cable with a USB-C connector for the iPad and a USB-A connector for the iMac. Strangely, the iMac only recognized the iPad when one side of the USB-C connector was up; when I flipped it 180°, the iPad would still charge, but it no longer connected to the iMac. Furthermore, the connection was very labile: just touching the cable lightly would disrupt it. The USB-C port on the iPad also felt wobbly and I could see that it was partly discoloured. So I brought the iPad to repair shop and they replaced its USB-C port. They confirmed that it was corroded.

Unfortunately, with the new USB-C port, the iPad won't connect at all to the iMac, although it still charges. I brought it back to the repair shop. They changed the USB-C port again, but that didn’t fix the problem. After some additional testing, they determined that the iPad will connect to a computer, but only if it's plugged directly into a USB-C port. It will not connect if it’s plugged into a USB-A port with an adapter or through a USB hub. I tried different adapters, different cables, including new ones, and nothing works. The iPad charges, but it does not connect to the iMac. Given that my model of iMac doesn't have a USB-C port, this means that I can no longer connect the iPad to the iMac by cable. (The people at the repair shop suggested that either the hardware or the firmware on the iPad may have some compatibility issues with the new USB-C port, and that possibly some other components might also need to be replaced, but they were not in a position to do so.)

Any idea what's going on?