ImGui is great, but it's designed rather for editors, tools and debug than for game purposes like menus, indicators, buttons with graphics and such things.
I checked some of code and later started writing my own GUI unit + LCL editor, probably the easiest solution. It's done in simple way, +- similar style as User137 code (NX).
From Pascal world is most advanced probably ZenGUI, what I found. With full exporter for events code (it generates unit).