iPadOS takes up 2/3 of storage space on iPad 128 Gig - 8th Gen - 15.7

You may need to backup the data on that iPad to Apple iCloud or to a Mac or Windows PC and then completely erase all contents and settings in that iPad, in the Settings app, under the General panel, Rest panel, then setup that iPad as a new device and thrn do a data restore from backup back to that iPad.

Good Luck!

Not sure.

After ANY iOS/iPadOS upgrade/update, you should ALWAYS perform a simple hard reset of your Apple mobile device.

For iPad models with a Home button, do a simple hard reset of your iPad by holding down both the Home and sleep/wake/power button simultaneously until your iPad goes to black and restarts with Apple logo, then release the buttons.

Good Luck!