Back up Ipad
How do I back up my ipad with a cracked screen?
iPad Air 4 Wi-Fi
If you can't access the iPad with the cracked screen, its too late now, there no way to back it up anymore.
Backups should be done while the iPad works correctly and can be accessed, as a preemptive measure not once the iPad is damaged.
If you can navigate the iPad, you can go to Settings ➜ Account (top of settings) ➜ iCloud ➜ iCloud Backup ➜ Backup Now. click here ➜ How to back up your iPhone or iPad with iCloud - Apple Support
If you did not turn it off, the iPad is set to automatically back up to iCloud when connected to Power and Wi-Fi with the screen turned off for an extended period of time, such as overnight.