To be frank, I don't find the motivation convincing. The motivation is
essentially a rant about the ecosystem of third-party libraries, but
provides no good justification for why something has to be in the
standard library. There needs to be a case study of how often C++
really is used for JSON, why it is unacceptable for people to use
third-party libraries, and whether adding it to the standard library
actually solves the problem.

https://xkcd.com/927/

On an editorial note, I'm not sure where you have your images from,
but those probably need sources. They could also use a dark theme
(pretty sure CSS media queries let you pick different images for
dark/light theme). Currently, I'm seeing dark-themed HTML but the
images are black text on white.

There are also accessibility concerns with providing images. I would
simply provide a formal grammar. People who rely on screen readers
cannot use these images, and an alt text isn't sufficient.