Should UI elements be marked as static in the inspector?

I’m using “Screen Space- Camera” for the canvas, should I mark it as static?

An excerpt from the documentary:

Static batching allows the engine to reduce draw calls for geometry of any size provided it shares the same material, and does not move. It is often more efficient than dynamic batching (not setting it to static), but it uses more memory.
In order to take advantage of static batching, you need to explicitly specify that certain GameObjects are static and do not move, rotate or scale in the game.

It can also affect the build size if you mark 3D Objects as static if there’s a lot of them, but since you only want to set UI emelents as static you should be fine.

So in general it is a good idea to use static batching if you are FOR CERTAIN, that this GO doesn’t transform or you don’t want it to (the Object will just stay in place, it can still be moved by changing the transform values in the inspector or moving it in the Editor but it won’t in the game via code or the like).

More info here: 4 Ways To Increase Performance of your Unity Game

and here: Unity - Manual: Draw call batching

Now in the case of Screen Space - Camera, the doc says:

in this render mode the Canvas is placed a given distance in front of a specified Camera

As long as the Canvas isn’t marked as static it should work, but if it doesn’t work or you encounter unexpected behaviours you should always keep in mind that this can be a source of the problem.

Next to the static checkbox there is a little drop-down arrow wich shows you everything that static batching affects when you tick that box, you can also just specify that some of them are static by clicking on individual items, but it’s a good idea to read and know about those options, because you will eventually need those in the future.