Henri here- I got a Numark Mixtrack Platinum FX, and none of the configs/mappings I found fully worked. I took the existing code for demo mode from here and merged it with this code. It now works. I'll save you the pain of figuring this out, and upload the files. Feel free to submit an issue if anything doesn't work.
To install these files, look at the official installation guide.
Ending2020's readme:
Mixxx DJ Controller Mapping for Numark-Mixtrack-Platinum-FX
Welcome to the Numark-Mixtrack-Platinum-FX-Mapping wiki!
This is a project based on the Numark Mixtrack Platinum from Matthew Nicholson. Thank you for your superb work Matthew! https://github.com/mixxxdj/mixxx/wiki/numark_mixtrack_platinum
I'm a nooby in coding and can use all the help I can get! Thanks! Ending2020