Log out is the last option in the main menu. On a mobile device, the main menu is accessed via the three line icon, bottom right.
Computer Mobile device
Some members on a computer will chose to have their browser zoom set high, or have an older monitor with low resolution, and so may not see the bottom of the menu. If that is the case, please be aware that each of the section headers in the main menu can be collapsed by clicking on them, which will bring the log out option into view.