iPad Pro 12.9" 2nd gen Stuck on Boot loop and bright spots on the left side

The “stage-lighting” issue is caused by partial delimitation of the screen backlighting. The screen is illuminated from LEDs placed around the periphery of the screen. When the fault becomes visible, you see bright patches of light around the edges of the screen.

This fault appears to be a characteristic of the first and second generation iPad Pro 12.9” - complaints of which of seen with some regularity.  The only resolution is screen-replacement - which usually entails and our-of-warratny exchange through Apple or an Apple Authorised Service Provider (AASP). The repair cost via Apple is typically c.60% of the “as new” price of the iPad - and where exchanged, you will receive a reconditioned iPad of exactly the same model and specification as the device that it replaces.

Given your screen issue, combined with other problems, it may be most cost-effective to cut your losses - and use the money that you would otherwise spend on a repair/exchange towards the cost of a much newer and more powerful iPad.

This is perhaps not the outcome that you were hoping to find, but many contributors here would advocate that you consider a newer iPad, instead of repairing the old, as the “smart” option.

Your iPad is out-of-warranty. Had you attempted to make a warranty claim whilst you were within the warranty period, you would have perhaps had a valid claim. After expiry of the warranty deadline, it’s simply too late.