Turn on Dark Mode
If you use your iPad Pro at night, you'll want to turn on the new Dark Mode in iPadOS 13. This is a great way to prevent a blinding white flash when you use apps.
Many apps now support Dark Mode, or like Gmail, they are rolling it out. Some users can use Dark Mode in Gmail now, while others may be waiting well into 2020 for the feature.
Go to Settings -> Display & Brightness -> Tap on Automatic or choose to always use Dark Mode. You can set this by sunset and sunrise or by specific times.