Mac M1 and Sonoma here.
After having performed Unmix song and drums inside latest Cubase 14, made extension permanent, saved the Cubase project and closed Cubase I found lots of really big files in the SpectraLayers 12 cache folder. It should be empty.
I remember a previous version (11?) had the same bug. It got got fixed but I still have the folder visible (on an external SSD) to watch it.