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".