I've found the AUTOMATIC BRIGHTNESS setting to be way too dark on all of my devices, past & present (about 10 & counting)., including HTC, SAMSUNG, MOTOROLA, LG & HUAWEI.
As for the other issues, I only have one suggestion, which may also cure the previous non-existent dark screen:
Perform a FACTORY RESET, especially after software/firmware updates. For reasons beyond my scope of comprehension,a reset cures a lot of these out-of-nowhere issues.
Just yesterday, I had to do this on my SAMSUNG GALAXY NOTE 8, as it wouldn't load ADOBE FLASH, for no explicable reason. The permissions for side-loaded apps was granted, yet it still rejected the installation.
Just one of countless examples of a FACTORY RESET correcting a problem.
Take care to back up any locally stored data (on-phone) such as contacts, pix, music, media, etc.... to an external source, such as your PC, or, cloud-based services such as DROPBOX/GOOGLE DRIVE, etc.......