Only "monocoque" designs use the panels as part of the structure. But normally they're bolted on. If you look at, say, https://www.paintedcarpanels.co.uk/ford%

Only "monocoque" designs use the panels as part of the structure. But normally they're bolted on. If you look at, say, https://www.paintedcarpanels.co.uk/ford%2Dfocus%2D2008%2D2011%2Dn%2Fs%2D%28left%29%2Dfront%2Dwing%2Dpainted%2Dpanther%2Dblack%2D%2D%2Dnew%7E854 https://www.paintedcarpanels.co.uk/ford%2Dfocus%2D2008%2D201... - left of photo you can see a "tab" extending from the panel with bolt holes, and top you can see a semi-circular pair of prongs. The panels are bolted on, and the bolts hide inside the engine bay or under other bits of trim. The Cybertruck deliberately uses flat panels for its "aesthetic", and I believe their material is harder to bend for purposes of making these little fixing points. Combine that with the polygonal structure and there's probably no other way to do it other than welding mounts to the back. Still a bizarre decision, though: what happens when you need to change a panel? How do you get them unglued only at the right time? How heat-sensitive is it?