MacBook Pro 2015 Keyboard and trackpad not detected once booted into operating system

Solution 1:

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.

Solution 2:

We had this problem, we took it to a service and they said this is a common problem with MBP2015.

There's a cable that connects the motherboard with the touchpad.

That cable can die over time.

They swapped it out and we could pick up the machine and it was up and running with working touchpad/keyboard in just 2 hours.