MacBook Pro 2015 Keyboard and trackpad not detected once booted into operating system
I had the same issue and was able to fix it. For everyone having this issue, try solution from here:
Press Shift-Control-Option on the left side of the built-in keyboard, then press the power button at the same time. Hold these keys and the power button for 10 seconds. If you have a MacBook Pro with Touch ID, the Touch ID button is also the power button.