As a temporary fix you can add photometric data for individual luminaires by going into Products>luminaires>Add...
Then Individual luminaire tab > 'Browse..' to find your file and open it > click 'Add>>' and click OK.
You should be able to use the custom luminaire.
I hope this helps until you know the folder location.
C:\ProgramData\Relux Informatik AG\ReluxData
For anyone who's interested.
Nice of them to change this location without telling anyone.
Only noticed this on the data update panel on the online update function.
ReluxDesktop personal luminaires are kept here: C:\Users\<your user name>\AppData\Roaming\Relux Informatik AG\ReluxDesktop\fremdlvk