Doesn’t sound like the clutch. Most likely a bad slave or master clutch cylinder not allowing the clutch to fully disengage. Another common issue is poor adjustment of the slave cylinder and clutch pedal.
for the slave cylinder get under the car and push the lever towards the rear of the car. It should hit the release bearing and still be angled slightly toward the front of the car from vertical (if that makes sense). If not, remove the bolt and nut securing the lever to the release bearing shaft (be very careful not to drop the nut into the bell housing!!!) pull the lever off the shaft and move it one spline forward. That should set the slave cylinder correctly.
The pedal can be adjusted by pulling back the carpet and sound proofing. With the pedal at ready it should measure 6 7/8” from the steel floor pan, if you have a workshop manual double check as my memory is faulty these days. (I’m sure
@harveyp6 will be along to correct my dodgy memory on the exact height) of it needs adjusting loosen the lock nut on the trunnion at the top of the pedal arm and use a screw driver to wind the master cylinder shaft in or out to get the correct height. Tighten lock nut afterwards.
As an aside, symptoms can of a failing clutch are normally no drive to gearbox or slipping under load. A clutch that doesn’t disengage (such as this case) are normally the clutch operation mechanism, which in the P6 is hydraulic. I’ve yet to see a clutch release bearing fail on a P6 as they are
very well lubricated.
quick edit: you’ll probably get more answers if you post in the
gearbox and drive train part of the forum. Where you can find
@harveyp6 guode to adjusting the clutch hydraulics
Clutch pedal height.