I would encourage not overthinking it...just go eat alone in Zurich. It's fine.
Here is tonight (Monday) at Hiltl. While i was there, about 10 people ate alone. Picture shows 4, plus me taking the picture. Don't worry, my Cola Zero was not lonely in the glass.
Also, I always forget how cool Hiltl is. If you are a woman from a country where drunk men in bars get "aggressively friendly" towards women who are alone (like in the US), Switzerland is not usually that place. And places like Hiltl will feel very safe. Lots of female wait staff and bartenders, and lots of females there with female friends. Very non-threatening. My wife is sensitive to this kind of stuff, and she loves Hiltl when she joins my trips.