The header style you have selected is hamburger menu style. The header version for the page is light. This makes the hamburger menu white. I changed it in the page’s settings > General > Header Color, to ‘dark'(screenshot). And now it is visible.
As described in my last reply, the color of the menu is defined by the header version. If it’s selected “header light” the color will be white, if selected “header dark” the color will be black (or any color you have set up in the settings).
Just go to page’s settings > General > Header Color (screenshot). Select dark.
-Customize the sticky header style in Appearance > Customize > Header > Sticky (screenshot).
