[Adoby]

I don't mean that you run calibre ON the iPad. Just that you control it FROM the iPad. I assume that there are VNC or RDP software for the iPad? (Spoiler: I just checked. Yes there are.) So you can read a book on your iPad and switch app to instead remotely control calibre on your PC from the iPad. And edit metadata as you like. I assume that you can even attach a keyboard and a mouse to the iPad and control calibre fully from the iPad.

Or you might even use the calibre reader app on your PC remotely from your iPad.

I wouldn't do it. But I don't feel any need to transfer metadata from my reader device to calibre.

Or skip the iPad and use some other device. Perhaps even one that can run calibre. Perhaps even a laptop or a hybrid laptop/tablet. That may or may not be an alternative depending on how important it is to be able to edit the metadata in calibre on/from the reader device compared to how important it is to keep using an iPad.