The major trouble with StackOverflow is that nominally duplicate questions may have different answers if asked on 2011 vs 2026 - and the trouble is that answer rankings (the thing that determines what answers are in the top) don't decay over time. So if someone try to answer an old question with up to date info, they won't garner enough upvotes to overcome the old, previously correct but now outdated accepted answer at the top. (even with a ranking decay, there is little incentive to give a new up to date answer to a established thread - people are more likely to contribute to brand new threads)

It would be better to allow duplicates in this specific case, but mark the old thread as outdated and link the questions in such a way that one can see the old thread and compare it to the new thread.

This is something I saw all the time. I’d look something up, knowing that there was probably an easy way to do <basic programming task> in modern c++ with one function call.

Find the stack overflow thread, answer from 10+ years ago. Not modern C++. New questions on the topic closed as duplicate. Occasionally the correct answer would be further down, not yet upvoted.

“Best practice” changes over time. I frequently saw wrong answers with install instructions that were outdated, commands that don’t function on newer OS version, etc etc.