Select elements in the sidebar, which is better?

So, my friend and I are building a web app and we were having a little argument. We need to have two select elements in the sidebar and one of them is not relevant to a few pages. Which of the following options is the best one ?

Firstly, we had the idea of having it on top and making the non relevant element disappear. It seemed pretty bad because it moves the elements under the cursor.

Secondly, we then thought of making the non relevant one disabled.

Finally, we also thought of putting the elements at the bottom of the sidebar. and then removing the non-relevant one

Which way would be the best ? Thanks in advance !