Whilst you appear to have a crack across the screen, this is an entirely separate issue to the bright patches.
This complaint, in context of bright spots appearing on the screen of an iPad, has been known to appear here with some regularity. This problem has been seen with the iPad Air3 and the iPad Pro 10.5 - upon which the Air3 is based. This is not to say that the problem is itself common, merely that the complaint appears to be common to these models of iPad.
Of complaints that have appeared within this community forum, the issue seems to focus upon bright patches (of varying intensity between affected devices) typically occurring in a region 1-2” above the Home button (as viewed with the iPad in the “Portrait” orientation - with the Home button at the bottom of the screen). In extreme cases, the patches extend further along the central axis of the screen. The bright patches correspond with components of the logic boars that generate heat - and this appears to cause issues with the diffuser that should distribute light uniformly across the panel.
In context of physical construction, the main logic board runs along the central spine of the device - flanked by two equal sized Li-Ion batteries. By contrast, most (if not all) preceding iPad models have their main logic board positioned along the right-hand side of the iPad, with a much larger battery/batteries occupying the majority of the remaining chassis.
Anecdotal comments (from reports appearing within this Support Community) suggest that when “inspected” by technicians, displays exhibiting this phenomena are generally considered to be fault-free - until such time as an inspection relates to a possible trade-in, at which point an affected screen has reportedly been described as having been damaged or defective, significantly reducing or eliminating any residual trade-in value.
The potential issue and its cause have never been publicly acknowledged by Apple.
The only remedy is replacement of the iPad screen. Given that you appear to have a substantial crack, a screen replacement is already required.
I hope this is in some way helpful to you - if only in confirming what is known about this issue.
