to fix the missing more section and customize button you can install/enable the cakeday plugin that puts the anniversaries and birthdays links in the more section and then it should reappear for you. the cakeday links can’t be removed using the customize in the more drop down. you can disable the cakeday plugin once you’ve fixed your menu. probably works with the docs plugin too but i didn’t check.
nonetheless this is a bug with the more section.