I asked 1 high-quality question in 2024, and it was closed almost immediately, and I haven’t engaged with the site since.

If someone with 20,000+ karma has their nicely-formatted questions closed so quickly, what must the newbies and rank-in-file encounter? This is probably a big reason why it’s declining.

It’s a high quality question, yes.

The close as already answered elsewhere is valid though. It’s not saying that the question is wrong; at least a decade ago StackOverflow explicitly allowed and encouraged asking the same question in different ways so they and their answers can be found.

It’s about operator precedence. And the referenced question asks the same thing, about ?? and a comparison operator.

The head note says:

This question already has an answer here:

Notably, it refers to answers, not the invalidity or duplication of a question.

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The header also mentions [previously] opinion based, so I looked into the question edit history. It most certainly was not a “high quality” question at the beginning - at the very least to the degree it looks like now.