Emoji does not work on my Mac Mini

Might seem like a small irritation, but has taken up hours of precious Googling time! I cannot get character viewer to display. 'Keyboard Preferences' – whenever I check the 'Show Keyboard and Character Viewers in Menu Bar' box, it spontaneously unticks itself when I move away from the tab. Even when ticked, it does not show the character viewer icon in my menu bar. When I check the box for 'Show Input Menu in Menu bar', it shows a flag rather than character viewer. the dropdown menu from the flag does not have the option to show character viewer. If I go Edit – Emoji and Symbols, nothing happens. If I use keyboard shortcut, the Edit button flashes blue as if it is doing something, but still nothing happens. I passed an Apple store the other day and popped in to ask about it, but she was flummoxed. I have fixed permissions etc. I don't have a great deal of tech knowledge, but can certainly get by, and I am sure it isn't just me being thick!