Yep that sounds like a first – the seat bolt. Very annoying position to snap a bolt in, but not the worst. Did it snap off because it’s all rusty/corroded or did you cross thread it and tried to wind it out?
If you can remove the seat cover (your doing that anyway) and can see the seat foam, not sure if you can lift the foam a bit to get access to the plastic seat tray. My idea would be to make up some wood chocks to somehow fasten the seat tray in a vice securely, then left hand drill bit drill out the bolt. Punch a dent into it first as a guide so the drill bit doesn’t stay and destroy everything else. Then again, if you have the seat cover and foam off/up (never seen it myself) you might be able to see how the nut is secured to the seat and remove it as well – replace entirely or work on removing the bolt away from the seat. Someone who has seen the naked seat tray might have answers to all these questions.