The battery in your unused iPad Pro is severely depleted. iPad batteries must be periodically recharged if they are set-aside for storage - or if they are infrequently used - as otherwise the battery will eventually become fully depleted through self-discharge. Li-ion batteries must never be allowed to remain fully discharged, as they may irretrievably damaged and may not recover.
Batteries - Maximizing Performance - Apple
Connect your iPad to its Power Adapter and leave the ipad to charge undisturbed for several hours, or preferably overnight. Given that you have an iPad Pro M1, this should have been supplied with a 20W USB-C Power Adapter.
Then, if necessary and while still connected to external power, try a forced-restart:
Force restart iPad (models with Face ID or with Touch ID in the top button)
If your iPad doesn’t have the Home button, do the following:
- Press and quickly release the volume button nearest to the top button.
- Press and quickly release the volume button farthest from the top button.
- Press and hold the top button.
- When the Apple logo appears, release the top button.
If the battery cannot be charged, the battery (or the iPad) will require replacement:
iPad Repair & Service - Apple Support
You might also visit the Genius Bar at your local Apple Store or Apple Authorised Service Provider (AASP) - where the technicians will be able to test and assess your iPad:
Genius Bar Reservation and Apple Support Options - Apple
For practical purposes, for battery service of qualifying devices, Apple usually exchange the iPad for a renewed/refurbished iPad of the same model and specification. The cost of the exchange is the same as would otherwise be charged for battery replacement.
