On a small display, tab to hamburger menu. Open burger menu. Continue to tab. Notice how it doesn't focus on the first menu item?
Also if you don't want to apply a focus trap when the menu is open, then don't blur out the content behind the open menu.
Otherwise, if you prefer to keep the background blurred out when the menu is open, then set a focus trap which will allow the user to cycle though the menu until they reach the burger toggle button via keyboard.
Tested on Brave and Firefox.
On a small display, tab to hamburger menu. Open burger menu. Continue to tab. Notice how it doesn't focus on the first menu item?
Also if you don't want to apply a focus trap when the menu is open, then don't blur out the content behind the open menu.
Otherwise, if you prefer to keep the background blurred out when the menu is open, then set a focus trap which will allow the user to cycle though the menu until they reach the burger toggle button via keyboard.