Your 3rd generation iPad Pro 12.9" was released in 2018. While capable of update to the most recent version of iPadOS (at the time of writing, this being iPadOS 26.2), given its age, you might reasonably anticipate that its software support lifetime is reaching its twilight.
Apple lists your iPad model as vintage - this effectively indicating that repair support is subject to availability of parts.
Obtaining service for your Apple product after an expired warranty - Apple Support
As such, repair by Apple might not even be a viable option. If repair service is available, whether or not the cost of repair would be economic is a decision only you can make. Speaking personally, if it were my money, I wouldn't bother with contemplating repair.
For practical purposes, in lieu of repairing and returning your own iPad, Apple usually exchange a qualifying 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 repair. Unless you have benefit of an active AppleCare plan, an out-of-warranty repair while expensive will be somewhat less than the cost of a replacement iPad.
If available, Apple offers a fixed-price price repair. You can verify eligibility and cost for your region/country here:
iPad Repair & Service - Apple Support
If you have an active AppleCare+ plan, the cost of repair is reduced to a small excess/deductible fee.
