So I took off the plastic shield on driver front side in order to inspect tran mount. (Yea... the rubber is all cracked)

But somsthing very curious. Sitting on the subframe I this long skinny bolt with a large washer, and a nut also not attached. Not sure how it has stayed there!

Appears to be:
M6 x 1 x 30 , with a 10mm head

Any idea where it might go to? I'm very curious if maybea mechanic a decade ago forgot to put a bolt back in somewhere lol

 

That would be a body or trim bolt. Probably got dropped and didn’t hit the floor. I don’t bother looking very long for dropped bolts.

 

That's been there a while. Probably a splash shield bolt,

 

Indeed, that is one of the bolts used to hold on the wheel well/shield, I believe around the front outer edge. Compare it to the ones you removed to get to that spot and I'm betting they are the same.
As for the nut, that looks like a size of nut used on the battery hold down rods on either side of the battery that pass through the hold down cross piece.
The battery hold down rod closest to the left front fender actually needs to be accessed from inside the wheel well. It may very well be the nut that's supposed to be on the end of that other end of the rod.

 

It' s pretty common to find loose nuts and bolts.

My favorite find was a 3 inch blade Spyderco knife.... Somebody cried when they lost this one...