EXPLANATION AND SOLUTION TO KEYBOARD BACKLIGHT AND TOUCHBAR ON STARTUP
When FileVault is enabled it encrypts EVERYTHING on the SSD and doesn't allow even the computer to have access to that data until you enter your password. That includes the software that loads during startup which would normally activate such things as the backlighting on your keyboard and the touch-bar. Which is why, with FileVault enabled, the login screen you get at startup is stored on Apple's version of their BIOS chipset, NOT on the SSD. After you enter your password on startup the decryption process begins and all of those necessary pieces of software start to load. Making your keyboard backlight turn on and your touch-bar activate. This is not a flaw or an oversight. It is how FileVault was built and how it protects against ALL AVENUES of data breech/intrusion. You'll be amazed at how hackers can devise code to use the backlight of the keyboard to hack into data on the storage device. So, now that you know why. Here are are your choices.....
1) IF YOU WANT TO MAINTAIN FILEVAULT'S SUPERIOR ENCRYPTION(RECOMMENDED BY ME)
STEP 1- DO NOTHING
2) IF YOU WANT TO HAVE KEYBOARD BACKLIGHT & TOUCHBAR FUNCTIONALITY
STEP 1- OPEN 'SYSTEM PREFERENCES'
STEP 2- CLICK 'SECURITY AND PRIVACY'
STEP 3- CLICK 'FILEVAULT' TAB
STEP 4- CLICK PICTURE OF LOCK (Located on lower lefthand side of current window)
STEP 5- ENTER 'PASSWORD'
STEP 6- CLICK 'TURN OFF FILEVAULT'
STEP 7- CLICK 'RESTART & TURN OFF ENCRYPTION'
STEP 8- YOUR BACKLIGHT AND TOUCH BAR SHOULD WORK ON STARTUP FROM NOW ON.
STEP 9- IF IT DIDN'T WORK BRING YOUR COMPUTER INTO APPLE. PROBLEM IS NOT FIXABLE.