Glass does NOT crack on its own.
Some stressor caused the glass crack. It could have been something that was happening with this iPad in the immediate past.
Something happened to this iPad or repeated “somethings” to this iPad for the screen to crack on your iPad Pro.
There is NO WAY or PROOF to prove ANY manufacturing defect.
NOT after 4 years of use!
Agsin, glass does NOT simply crack all by itself.
Sorry.
This iPad is long out of warranty and with this crack, there will be NO trade-in value for this iPad, now.
It is either attempt to get this iPad year and model replaced ( the costs will be a screen crack repair costs which, out of warranty, will cost approximately 60% of what that iPad Pro originally cost ) or forget ANY trade-in money and “bite the bullet” and purchase another new iPad OR purchase a “newer”, refurbushed or newer, used iPad model.
Either way, this will be an expensive replacement cost proposition.
Sorry.
There are PLENTY of less expensive, newer, older iPad models that can run the latest, current versions of iPadOS.
If you need OR ONLY able to purchase older, less expensive iPad models, look at older iPads from 2014 and later.
All of these older model iPads below, CAN run the latest releases of iPadOS 15.
2014, 9,7 inch screen iPad Air 2 models ( NO Pencil support )
2015, 7.9 inch screen iPad Mini 4 models ( NO Pencil support )
2015-2017, 12.9 inch screen iPad Pro models. ( 1st gen Pencil support )
2016, 9.7 inch screen iPad Pro models ( 1st gen Pencil support )
2017,10.5 inch screen iPad iPad Pro models ( 1st gen Pencil support )
2017, 9.7 inch screen iPad 5th gen models ( NO Pencil support )
2018, 9.7 inch screen iPad 6th gen models ( 1st gen Pencil support )
2019, 10.2 inch screen iPad 7th gen models ( 1st gen Pencil support )
2020, 10.2 inch screen iPad 8th gen models. ( 1st gen Pencil support )
2019, 7.9 inch screen iPad Mini 5th gen models ( 1st gen Pencil support )
Get the largest internal data storage model you can afford as NO Apple iOS device has ANY expandable storage.
I am sorry that you had to learn all of this.
Sorry & Best of Luck to You!