pressing letter keys doesn’t work, but pressing number keys above the letter keys does work; software problem or … ?
OK what about the function keys
If that’s OK do you mean no keys below the numbers ‘work’ or just the letters i.e. space, enter, ctrl etc. do work
Which ever I would imagine it’s a keyboard connector/cable that may not be seated well enough.
Although hopefully you will not have to change the keyboard it may be usefull to see this guide about replacing it as it will show how it is connected anyway.
You may like to start with this?
This guide is for the ‘input cover’ replacement which is very simple and shows the connection between the ‘input cover’ (keyboard, trackpad and power button.
You should contact Support: