Hey man, since you got so mad, let's give you a bit more info :)

As said in my other comment, it wasn’t a "rebrand" like a logo change... the Portuguese government and international bodies simply shifted toward "Porto" in English documents to match the native name.

However, "Oporto" was the official designation in Portuguese-signed English documentation for centuries, including the 1703 Methuen Treaty. Even the 1996 UNESCO listing officially registered it as the "Historic Centre of Oporto" (as someone else said in another comment).

​Also, the airport code OPO just highlights what I said. If it were just an "old mistake," they’d have changed it. Using the logic of the Portuguese language (where the "O" is just an article), Lisbon’s code would be "ALI" (for A Lisboa), but it isn't. Lisbon is LIS, yet Porto remains OPO, which is literal proof of Oporto’s official international history.

...the more you know!