Perhaps confusingly, the term "immediate mode GUI" usually describes an API style. NOT an implementation detail.
It suggests a particular implementation, but in practice most nontrivial "immediate mode" GUI libraries (including egui [1] and the famous Dear-IMGUI [2] [3] ) retain some "shadow state" between frames. The existence or scope of that state is a (sometimes-leaky) implementation detail that shouldn't distract from the fact that the API presented is still "immediate mode."
It suggests a particular implementation, but in practice most nontrivial "immediate mode" GUI libraries (including egui [1] and the famous Dear-IMGUI [2] [3] ) retain some "shadow state" between frames. The existence or scope of that state is a (sometimes-leaky) implementation detail that shouldn't distract from the fact that the API presented is still "immediate mode."
[1] https://github.com/emilk/egui#ids
[2] https://github.com/ocornut/imgui/blob/master/docs/FAQ.md#q-a...
[3] https://github.com/ocornut/imgui/wiki/About-the-IMGUI-paradi...