I too miss the traffic, but maybe it's not really a sign of the forum declining, but rather morphing. Let's face it: for some tasks, an AI agent is at least as good as any advice found here, plus it's much faster. So yeah, that kind of traffic is going to drop off.
BUT:
Members of this forum have much more to add than just their ability to write/solve algorithms, or serve as a document lookup. Over the years, many of my questions have been subjective, and the answers benefitted from the real-world experience of more senior Qt-ers. AI can't replace that.
So yeah, there'll be less traffic, but what remains is still quite valuable.