Hi AER55,
Thank you for reaching out Microsoft Community.
In order for you to turn on the backlight feature of the Surface Pro Typecover, kindly visit this thread>>https://answers.microsoft.com/en-us/surface/forum/all/surface-pro-5-type-cover-backlight-keys-not/d8a6d290-eae7-44e3-930b-2e5ccae3e898#:~:text=You%20only%20need%20to%20use%20the%20Fn%20key,should%20cycle%20through%20several%20levels%20of%20keyboard%20backlighting. for instruction.
If that helps, feel free to mark this post as an answer. Otherwise, don't hesitate to respond to this thread if you need further assistance.
Kind Regards,
Crest