[pb82]

They are very different in terms of usage. Dear ImGui is an immediate mode UI library which means that rendering and evaluation happen at the same time. You write for example:

if (ImGui::Button("X")) { //pressed handler }

This renders the button and handles its state at the same time.

Qt is a more traditional callback based UI although with their own signal/slot system which has nice features like thread safety built in. I last used Qt a while ago though so maybe it works different nowadays.