QRs are a lot more complex than that, though. It's not a symbol mapping, it's an encoding of a binary string, which then pieces of map to characters. And even if they do figure out how to decode them, they'll just get the urls, which won't mean anything without understanding the internet.

If human civilization loses continuity, we're going to lose so much knowledge in the process. If another civilization proceeds us (either post collapse humans or some new species that goes down the big brain plus societal knowledge), they will truly live in a situation where there were ancients unfathomly advanced. It's possible that some of the things we're capable of now are forever the high point and no life on earth will ever understand that thing the same as we do now or better.

Though a lot of it will require a certain amount of advancement to even understand how advanced it is.

That said, any ink-based QR codes aren't going to last for thousands or even hundreds of years. Engraved ones might, but the ink ones will probably depend on some advanced molecular/chemical methods to even figure out that they were once coloured black and white.