New or shedding textiles can transfer loose fibres to other items in the same wash. Fluff attached to a dark garment is a different result from detergent powder or damage to the fabric itself.
Understanding this situation
Inspect the material gently after the wash and consider what else was in the load. Towels, fleece and other lint-producing items do not always combine well with smooth dark fabrics. The wash may have released normal loose fibres rather than manufactured new debris, particularly when the issue follows a new household textile.
A useful next step
Separate known shedding items according to their care labels and use the correct programme capacity. Check pockets as well, because tissue can create a similar-looking mess. If fibres continue to appear after the obvious source is excluded, retain a clear description and the recent load history instead of repeatedly adding cleaner without knowing what the deposit is.
Manuals and supporting guidance
Model-specific instructions take priority. These references support the practical principles discussed here; they do not diagnose your appliance.