PostgreSQL has been around for almost 27 years (and even longer, if you include the Ingress and Post-Ingress eras). And things, well things, they tend to accumulate, to quote Trent Reznor, heh.

On a related note, one could say that the C++ Core Guidelines[1] at least partially represent such a list. 55 matches for “don't use” and 247 for “avoid”, although not all of them are about language features, obviously.

[1]: https://isocpp.github.io/CppCoreGuidelines/CppCoreGuidelines

I think that every platform that's old and has backwards compatibility has to have such a page - because there inevitably will be features for which we (now!) know that there are better ways to achieve the same goal, but they have to stay there for compatibility reasons.

To be fair, some of them exist in PostgreSQL because it tries rather hard to conform to the SQL standard.