FWIW I have noticed from time to time that when I am (deliberately, on my smartphone browser) using mobile view, that the 3-lines aka "hamburger" menu, looks different and in particular is lacking the "view full site" option. This seems to happen for no rhyme or reason, with no change in behavior pattern or settings etc. on my side, and also seems transient, going back to the way it normally looks (again with no changes other than the passage of time).

Previously reported at: "View Full Site" no longer works (momentary - resolved)

but since it's rare and intermittent, I realize it's difficult to troubleshoot...

As for the original issue, I see margarita girl already found it, but for an alternative to the 3-lines menu, refer to post #3 here: Switched to mobile view and can't switch back to desktop view