Game engines (at least the lightweight ones) seem good for cross-platform graphical apps in general but the idea of redrawing a static GUI at 30 FPS just sounds too inefficient to me.

You're absolutely right. So I do without 30 FPS.

We're all up this tree where we want all the features we're used to and we're willing to put up with software bloat and insecure software and sprawling supply chains to get it. I'm not. So I start with something minimalist and do what I can within it.

One of my inspirations is http://akkartik.name/illich.pdf

Does this mean that you're rendering at 1fps, 10fps or something?

Is it an artificial limit you put on rendering?

Do you have button animations at 30 FPS?

All I meant is, if drawing too many things overloads the system so it can't render at 30fps, that's fine, I build things that don't look bad if the rate drops. I can't do action games, high-speed video, a few other things. That's fine, I can still do lots of things.

You can lower the frame rate when the window is not focused, or entirely avoid drawing if it's not visible.

Well, that's certainly an interesting approach!

I believe game engines usually draw to a texture then display the texture, reusing it on subsequent frames, but if they don't, that wouldn't surprise me. UIs don't take long to draw, so drawing at 60fps is often quite cheap.