The collapsed navigation menu in Optica is set to a static position by default, meaning that you can only access it by scrolling to the top of the page.
However, with a simple custom CSS tweak, you can set the burger menu to a fixed position, that stays aligned when you scroll:
/* Fixed burger menu */
This way, your menu is always visible and accessible when visitors scroll through your blog. You can see an example here.
This tweak will also affect the Search menu, that replaces the burger menu when the navigation is expanded.