Hm, I don't know how to answer that. Maybe some examples will help?
For example, I'd kind of like to learn about some web programming. I have some ideas for a photo file browser/slideshow application that would be useful for me, so making a web app to do that is an idea I could use to explore some web framework.
Another example, I'm into Street Fighter 6 lately. I've been thinking about how it handles input for choosing moves in a way that "feels good," and how to specify hit detection, handling move priority, etc. If I wanted to learn a new language or graphics library, I'd probably try to write a simple fighting game to explore those challenges. This would just be a toy, not a serious project. The end goal would be to learn whatever library or language, and then forget about the project, except as an example of something I made with the library/language.
So... I guess I just kind of keep a list of stuff that seems useful/interesting in my head, and grab something from that list when it's time to go learn something new.
> but now my interests often take me away from the computer screen
Yes. I'm the same age, though I don't have any kids, and I feel the same way. With programming as a job, it's stopped being a hobby for me. I kind of miss it. Now I do guitar and woodworking instead :) but that doesn't help with the career.
As a follow up a question. Many of you said you pursue your interests and passions, exploring them in personal projects. Feels weird to ask but, how do you identify/kindle these interests? I feel like early in my career they came fast and easily, but now my interests often take me away from the computer screen.