popular imgui toolkits like dear imgui (fortunately, nobody yet argues that dear imgui isn't really imgui) also actually retain some per-widget state

i would say that the key question is whether widget deletion and updating is implicit or explicit; it's a question about how the api is designed, not how it's implemented

with immediate-mode graphics like <canvas> or windows gdi, if you update the screen and forget to visit a certain rectangle, that rectangle disappears from the screen. the same thing happens in an immediate-mode gui if you are drawing a window and forget to visit a certain checkbox. both whether it appears or not, and everything about how it's drawn, are guaranteed to be up-to-date with your

with retained-mode graphics like svg or tk canvas or current opengl, if you update the screen and forget to visit a certain rectangle, by contrast, that rectangle stays exactly the same as it was before. the same thing happens in a retained-mode gui if you are drawing a window and forget to visit a certain checkbox: the checkbox is displayed in the same way it was displayed before, and it may be outdated with respect to the program data it's nominally supposed to represent

omar's explainer at https://github.com/ocornut/imgui/wiki/About-the-IMGUI-paradi... pretty much agrees with the above, though he goes into a lot more detail. similarly casey's talking-at-the-camera video in which he popularized the concept https://youtu.be/Z1qyvQsjK5Y?t=6m30s

so it should be apparent that react falls solidly on the imgui side of the line, which is why people use it