"in game" ui VS "main menu" ui

Just wondering how the two differ in development?

My main menu UI is a scene with its own camera, canvas, panels…etc…
On “load level” button, it loads the player/level scene.

How would one approach the “in game” ui?
Does it attach itself to the in game camera?
Will it be portable to different levels and scenes?

Thanks for any input, links, or threads. <3

ah hah, figured out the canvas attaching to the player camera in world space.
<3