MacBook Air 2018 typing wrong letter
I would suggest you check your keyboard with OnScreenKeyboard. You can hit one letter C and see whether it is pressing on correctly or not.
To enable the onscreen keyboard in case you don't see it:
Open System Preferences and go to “Keyboard”, and look under the “Keyboard” tab
Check the box next to “Show Keyboard & emoji viewers in menu bar”
Pull down the newly visible Keyboard menu and choose “Show Keyboard Viewer”
After you conclude with this, you can try the following solution, it is a bit weird but have seen working for few people.
Weird solution
Let me know how it goes.