That is one of the things I really hate about the iPad.
Apple has an SD reader for lightning. The iPad with USB-C supports standard SD readers. From the hardware side, this is no problem.
Except that the software is missing. The SD in the reader is mounted to the internal Unix file system, but no end user software can access it. All one can do is copy the content of the DCIM folder to “photos”.
If you have a wireless server which can read SD cards, you can access the data in the “files” application (somewhat, it is not always very convenient). But you cannot do that for stuff connected to the lightning port.
For Apple, it would be trivial to access the mounted SD card from the “files” application, next to the files in the cloud. Users are still waiting for that.
