I make WordPress and ClassicPress plugins. Most of them I made years ago and they do everything I want them to do. So really it's all about maintenance, small bug fixes and the occasional feature to be added. Keeping up with the times, pretty much.
Yet, in the current climate of developing any software it seems mandatory to keep adding features, to keep rewriting code over and over. I don't want to add more features unless it's super useful. And rewriting code for the sake of making an update, well, that's no update at all.
Plus, I don't believe in endlessly rewriting code. If it works, it works. And if it works efficient, fast and intuitive - There is no real need to force things and potentially create problems.
And then the real reason for the question. If a plugin is not updated in say 3 months people might think it's not maintained. Less people downloading means the whole project disappears into obscurity, which is not desired either.
Well, you might think, replace bits and pieces with frameworks then. Or update dependencies and frameworks. My plugins have no dependencies besides what WordPress includes. Nor do I use frameworks. What? Yeah, I'll write my own code, thanks!
Actually I do use a few 3rd party 'scripts' in one plugin. Some Javascript bits and bops and a PHP thing. I guess those are kinda framework-like. But as long as the feature using it is fine, there is no real need to do anything with it.
Add AI perhaps? Well, let me say this about that. No!
So what do you do for updates for a plugin that's feature complete?
I've been rewriting some older parts with more modern code. I've updated database queries to be more efficient and use new things I learned. Sometimes I have an idea to re-arrange a dashboard a bit to make it work better or more logical. And, sometimes a user comment or complaint comes in with genuine good ideas and I'll add that or make changes based on that.
But for all the time in between? Minor refinements and tweaks it is...