Seems many have this issue. Me too. But I got to find my issue to be a glitchy connection of the trackpad cable. So I have now added extra padding to the shield to make it firmly pressed towards the motherboard. And keyboard and trackpad is working once again. So basically follow this guide https://www.youtube.com/watch?v=FzcBL1NB... See the shield in the middle of the motherboard, That is the one that needs extra padding to press down (or up when you turn the computer around).
for me the issue is a glitchy connector for the trackpad cable. Sometimes it works when I press down the frame between the trackpad and spacebar. Just now when I followed this guide https://www.youtube.com/watch?v=FzcBL1NB... I realize that the reason it works is because the connector is pressed into the socket. But then it stops again after a while. So today I removed the connector shield and added extra padding to see if that stops the connector to stop dropping out of the socket.