The problem is as follows.
iPhone 14 Pro, installed iOS 18 beta 4.
After locking the screen, the brightness resets to the lowest value. This happens every time the phone is locked.
The Brightness Resets To The Lowest Value.
The Developer Forums aren't really the right place to raise bugs in a new version of an OS. Apple's engineers aren't reading through these pages waiting to see if anyone's found a bug before they fix it.
These forums are for third-party developers writing apps for Apple's platforms to discuss issues with their code.
You need to raise each issue you find separately at https://www.apple.com/feedback/ You can post the FB numbers here if you want, so that others can link to them.