So I haven't been a C++ programmer for almost 20 years now (I would have considered myself very experienced with it at the time) and STL was the Standard Template Library for me back then. Is the Standard Template Library no longer in (widespread) use? Would any modern C++ programmer use it anymore?
The STL was standardized and made part of the standard library in 1998. So no it hasn't been a thing in more than 20 years.
It was around 2003 when I noticed people start to take issue with calling the standard library templates the STL. IDK why. Used yes, referred to as the STL not unless you like hostility from the language lawyers on stack overflow.