When playing a single player trip, you cannot quit to main menu easily without losing progress made on the trip. You are only given the option to abandon trip (and lose progress) or resume when in the ESC menu. You can still get this behavior if you close the window or tab that geoguessr is on and open a new link. This behavior should be inherent to the game menu to begin with considering that your progress is saved when you close the tab and on reopen it lets you be in the main menu ready to resume at any time.