Ehhh. Integrating an old C++ library into a new project may be difficult due to build systems or not useful due to dependencies.
However if you want to take an old C++ game written in 2004 and ship it on modern platforms and consoles you only need to update a very small amount of platform specific code.
Updating a 20 year old C++ project is probably easier than updating a 3 year old web app.
Tbf if you’re just looking to run an app on newer platforms you’d likely not need to do anything with the web app. They have a lot of issues but once stuff works it’s usually a very long time before it doesn’t.
It would probably still be harder to add a new dependency to a 3 year old web app than it would be to integrate a 20yo C++ project though, I agree with you there.
imo that would be a "forever program" not really a "forever language." The lack of standard packaging and terrible paradigm of shared dependencies has made C/C++ incredibly fragile and non-portable when you need something from years ago to compile today.
However if you want to take an old C++ game written in 2004 and ship it on modern platforms and consoles you only need to update a very small amount of platform specific code.
Updating a 20 year old C++ project is probably easier than updating a 3 year old web app.