We use custom inspectors built using UIElements and not IMGUI. I do not know whether Odin allows nested UIElements within their custom inspectors. To my knowledge UIElement can nest IMGUI but the other way around is not possible.
If you are not familiare with UIElements it is the new way Unity draws the Editor since 2019.4 when they redesigned the Editor. I believe it has been renamed to UI Toolkit recently as they plan to use the same technology for in game UI too in the future:
