This is so helpful, thank you very much! No and that is precisely the problem, the 8mm hex wrench (with a 90 degree grip) does not slide all the way in (i.e. around the bolt), it barely fits the tip of the truss rod, which is precisely why it is impossible to rotate in the first place, let alone if it’s stuck due to years of inactivity..
Sounds like you may need to get creative, effectively making your own wrench by cutting down an 8mm deep socket to fit and drilling it for a handle. Once you've got the old one off you could use spacers/washers under the nut so the regular tool fits without bottoming out. I've had that problem.
For now I have ordered a 9mm wrench (also with 90 degree angled grip) which should arrive in a few weeks. So lets see if that does the trick.. if not, then I’ll try to get creative yeah.. Apparently super easy to find 8mm or smaller wrenches for truss rods with next day delivery but very few 9mm truss rod wrenches out there, hence the wait time. We shall see - thank you all for your suggestions