In my experience what Paradigm2020 describes is very much the norm around the world.

> and briefly worked in a bank in,

I suspect this might be where the confusion stems from, if you're thinking of places where people go to banks you might be thinking a bit too fancy.

I'm thinking of stuff more like this https://www.youtube.com/watch?v=iCDQpm6f_pU

>According to that article it has nothing to do with condition, but with the lack of anti-counterfeiting protection on older notes.

I'd say the age of the money has everything to do with condition, and it matters a lot.

The claim I replied to was that: "in most of the world a $100 note is only worth $100 if it's in basically mint condition"

Somaliland is pretty extreme example and not representative of "most of the world". It is extremely poor, isolated because almost nowhere recognises it as a country which cuts it off from payment systems and currency markets.

I have no idea whether they claim is true or not in extreme places, but those places are not "most of the world".