I had a very strange issue with my iPad pro. No app would open and the home screen didn’t load properly. And yet I could open the app switcher and control center (just no apps). I also couldn’t get the power off screen (I even learned that control center has a power off button!). So, I took a day to run down the battery enough so I could reboot it. Now, it’s fine — I’m using it to post this — but I’ve never seen an issue like that where I couldn’t even force a reboot.