I think a lot of sellers do themselves a disservice by declaring their cars to be unfixable.
Seems to be a much better idea to say “it’s bad, I think it’s probably only for parts” and then take photos and let the buyer decide.
I’ve bought and fixed plenty of cars that the seller has said “can never be registered again” when in reality it just needs a couple of balljoints and a set of tyres…
Not sure if this is the case this time around, but if you already had a good interior or wanted to turn it into a race car, it would be a much more viable project.