NOTE: My original answer addressed only the cargo cover attachment point.
If you're trying to secure the tailgate strut attachment point:
I can't see any way to proceed that doesn't involve removing the plastic trim from this area. It isn't super difficult but it will be tedious to carefully remove the brittle plastic fasteners holding the trim in place and trying not to crack the equally brittle trim plastic.
With the plastic trim set aside, you'll have more room to maneuver. If you look at the bolt coming out of the tailgate support strut, it's fairly slim (it's not a toothpick but it's definitely not a motor mount bolt). It's also actually not a bolt: it's the ball end of a ball-joint. You won't need to put a great big nut on it once you have a secure mounting point.
With your situation, the mounting point is the problem. If you look at the sheet metal that the strut was attached to, it also isn't beefy. You don't need a lot of structure there but you do need some. My previous points about "maybe a washer will be sufficient" would apply to this situation except for one problem: movement.
At this point, my expectation is that an unsecured attachment point will have enough play that the tailgate will flex and rattle at every opportunity. A better solution would be to drill out a thin piece of sheet steel that has the correct spacing for both bolts (cargo and strut).
You'll then need to attach that patch to the sheet metal. It's possible that a welding shop may be willing to attach that to your car in the right location for a decent price but I don't know what your market is like. If you're not going to weld the patch in place, it's possible JB Weld (or the equivalent) might hold the patch in place but I'll let you make that call.
Once you've patched the hole, you'll have a backing plate to which you can secure the strut and the cargo cover attachment point.
If you're only trying to fix the cargo cover attachment:
I have a car from the next model year so I'm pretty clear on what you're looking at there. It looks like the bolt just pulled right through the sheet metal, pulling loose the interior trim plastic in the process. In fairness, that plastic is getting pretty old so some brittleness is not unexpected.
That bolt isn't a load bearing piece. It pretty much exists to stabilize that piece of trim plastic which is itself an attachment point for the cargo cover. No real stresses should be expected.
My suggestion would be to see if you can loosen the trim plastic just enough to slip a decent sized washer and bolt back behind that hole. You'll need to loosen some trim retainers (they look like big plastic buttons along the trim). Note that they will also be quite brittle with age so it's not a bad idea to pick up some cheap spares.
If you can get a bolt with a washer to support it back there, you should be able to slip the cargo cover retaining piece on and apply a nut with appropriate amounts of super glue to hold the whole assemblage in place.
