Tramontina lid stuck to pot
It seems really unlikely it somehow rusted shut or anything like that while you were boiling, so it seems most likely that there's just a partial vacuum inside. While boiling, it'd have been full of hot air and steam, and now that's all cooled down, and the steam has condensed, so it could shrink down you end up with low pressure inside sucking the lid down. It's a bit surprising that the seal is good enough to hold the pressure for this long, though!

In any case, if that's it, assuming there's still liquid in it, I'd try just heating it again. That would increase the pressure inside, hopefully back up to normal, enough to let you get the lid off. I'd also try twisting and angling it, because if that's it, all you need is a tiny opening to equalize pressure.

If this does turn out to have been the issue, you could probably avoid it in the future by opening the lid immediately when it's done.