I think this is a biased view held by people who migrated to Mastodon. In my experience on Twitter, the coding topics are as lively as ever, particularly around Web development. Personally, the introduction of the "For You" page has triggered me (very low following, previously inactive) to interact with accounts just because the algorithm does such a good job of surfacing relevant niche technical content for me.

Me: I couldn't speak about "coding twitter" in general

You: I think this is a biased view held by people who migrated to Mastodon.

Me: ???

Fair enough :) I suppose we agree then.

I don't know about Apple Twitter myself, but Web Dev Twitter seems more active. Infosec Twitter was a notable niche that loudly proclaimed they were moving to Mastodon but in fact many of them are still quite active on Twitter.