append scene / replace texture. when loaded do next step action?

Is there a way to know when a texture or a append scene is loaded/rendered on the screen ?
something like “when rendered do” ( not “when loaded do or once ready do”, This two are only useful when you need to know the download status)
We want to use this to trigger a feedback status on the app because when verge3D is processing FPS drop drastically and we want to lock UI during this time.