Tried DFU. Haven’t had any luck thus far.
One thing I noticed yesterday: I tried connecting the iPad to a MacBook (USB-C → USB-C). The MacBook seemed to recognise the iPad as a power source— it showed a charging indicator, although it also showed a message to say it wasn’t charging. So the port isn’t completely dead? DFU still wouldn’t work, and the iPad ignored the Mac— no charging indicator on that side. Also, having it plugged into the MacBook ran the battery down. I’m now at 24%. Stumped.
I’m appreciating all of the suggestions, nonetheless (thanks to @MartinPacker also). Also learning to appreciate my iPad Mini again…