In practice there is always a loop. I believe the point flohofwoe was making is that with an immediate UI you don't have to even touch events in your immediate UI code (they are abstracted away, if needed, in a pretty clean manner, IMO), so there's no need to do anything to get a "sane event loop". I might be wrong about what's his point though.

There's a loop yes, but not an event loop - the other argument is that you can have a loop that runs every frame, and you just rerender the whole thing

Not really. To expand on my response: In practice there is always the operating system's event loop, both in retained and immediate mode. This is true for all mainstream operating systems.

I mean, that's just being overly pedantic. Surely you see a difference between these two pieces of code?

    while (true) {
        redraw();
    }

and

    while (true) {
        waitForAndProcessNextEvent();
        redraw();
    }

Please don't call me pedantic.

What I am explaining is that in practice you have to use the second code, because of how operating systems work. This can be handled by a windowing library (SDL, GLFW, Sokol), and the adapters for libraries like Dear Imgui, Nuklear, etc. also expect the second code.

There are ways to skip processing events in some OSs, but this is not really advised by OS writers, and in some cases you will get subpar experience, apps that don't close correctly, etc.