As many know Fairlight - and audio recording in DR in general - ever since v.12 has been buggy, for many we can't even get it to recognize an audio input to do something as simple as recording a VO.
As I've suggested in many posts until these issues get solved (if ever) the only solution is to record externally from DR/Fairlight and import those files for final tweaking. So for Mac users there's a great solution at hand to do the task easily: "Audio Hijack" -
https://rogueamoeba.com/audiohijack/I use this to record VO just like using a channel-strip, like ART's "Voice Channel", but it's far more versatile. You can setup input gain, EQ, compression-limiter, noise reduction... just about any preset you'd need to create perfect VO and not need to do any tweaking after, just import into DR and get to work. And you can preview "wet" through the modules in real-time, so you know what you're getting before you lay down any tracks.
Included is a screenshot of how I've setup my recording session with the app, which allows any of the built-in modules to be pulled out of the frame and enlarged so you can see details for each easily.
This is the life-saving answer to not being able to get Fairlight to work properly. Sorry, don't know of a similar app for Windows but I'm sure any of the available DAW's would do the trick.