My 2017 iPad Pro was updated 2 days ago to iOS 12.4.1. Since then, it has been almost continuously rebooting whenever I try to power it up. I have managed to shut down all open apps, have hard rebooted several times. Cannot get it to stay on long enough to do other diagnostic checks on battery life, remove apps etc. How do I fix this?
It is likely you will have to put the iPad into Recovery Mode. THat will restore the iPad to it's clean factory state. EG anything on the iPad will be wiped out, so I hope you have a backup.
The iPad pro is a bit of a three finger salute to get it into recovery mode:
Hold the Sleep/Wake button, the volume up or volume down button (at the same time) until you see power-off. Use the power-off slider to turn off your iPad. Then connect your iPad to your computer while holding down the Sleep/Wake button. iTunes will ten prompt you to restore the iPad.
That is assuming there is nothing else wrong with it. If that works, then restore the iPad from your backup once it has been factory restored and you should be good to go.
If that fails let us know, but it may be time to take it to an Apple store or Apple repair shop.