Need some info and some advice with my clutch.

Hey, so I have an old 1980 Porsche 928 with a 5 speed manual transmission in my garage that's been sitting there for about 10 or so years. The car has been covered and out of the sun for that time period. I've got almost everything back to the point so that I can try to turn it on, but I'm having some issues with the clutch. The clutch is somewhat difficult to push back, but once you move it, the clutch can engage , but after it just throws the pedal to the back of the bay. It won't come back forward is what I'm trying to say. It just launches itself back. And I have no idea what could be causing it. I'm really needing some insight from the veteran car guys. Also I have no idea if the car is a mechanical or hydraulic clutch.

Clutch is hydraulic. There is a master cylinder actuated by the pedal at the firewall and a slave cylinder at the end of a hose at the bell housing. The seals in either or both have likely failed after sitting for so long, or the fluid has leaked out. At a minimum you will need to fill the system and bleed it. May need to rebuild/replace either or both cylinders.
While I enjoy this site, it is not very active. You may get more by posting your issue on the Rennlist 928 Forum. rennlist.com/forums/928-forum-69/

A "while you're there" task is to replace the small bit of hose between the reservoir and the clutch master cylinder. If that hose leaks all the fluid in the brake master cylinder will leak out.