The iOS 13 announced back in June at WWDC is finally rolling out with a system-wide Dark Mode, Apple Arcade, and new Memoji customization. It also comes with new Maps and Photos apps and adds swipe typing to the iOS keyboard. Besides, it makes Face ID 30% faster.
The iOS 13 is compatible with a total of 15 devices, which include:
In addition to iOS 13, Apple has also started seeding watchOS 6 for Watch Series 3 and 4. Watch Series 1 and 2 will get it later this fall.
That said, Apple will release iPadOS and iOS 13.1 on September 24, which is six days ahead of the originally planned rollout.
I don't have any heat issue on my 6S. Battery drain was already there as I have an aged battery and use Battery case. Generally the phone is faster and smooth
If you go to Accessibility > Display & Text size there is an option to increase contrast. By doing so it becomes a bit more gray.