You should be able to pull the slave cylinder off the bell and step on the pedal to watch it move. The rod should move out about 3/4". If its moving out, the pressure plate or throw out bearing has an issue. The last 3 clutches I've replaced had pressure plate and/or throw out bearing issues, and all of them quit disengaging. Usually the hydraulic part of the clutch system either works or it doesn't, not much can partly fail.

Two nuts and a pedal push will tell the story. Gene