Some ideas for (adult) toothpaste flavours that aren't mint:
Cherry or other fruits like apricot
Rose or any flower or a mix of flowers
Individual berries or mixed berries, but not overly sweet or weirdly textured like kid's toothpaste is
Any herb or spice actually, I already mentioned mint, cinnamon, anise, basil, & ginger, so why not include chai mix or cardamom, rosemary, fennel etc.
Adult versions of kid's flavours (so less sickeningly sweet, more options for texture rather than that horrible gritty gel in that annoyingly shaped plastic squeeze bottle) including but not limited to: watermelon, bubblegum, & strawberry
I'm just throwing out ideas here. Maybe I'll become an entrepreneur by accident.