I have watched a quite a few of YouTube on this S88 MK2 keyboard but none talks about these section of lights. I'm not sure what exactly it does.
That's the "touch strip". You can program it to send MIDI messages in MIDI mode, and I think some instruments use it too. Check out the manual here - KOMPLETE KONTROL S-Series MK2 Manual English (native-instruments.com) and search "touch strip"
Awesome, thank you! I'll check the manual in the link.