I like your style. Hanoi is a major tourist city, so I think you are really missing your stated goal because locals are familiar with tourists and the wants of tourists. Your desire for a cafe or bar says something? In my experience most cities in the world have a sameness that makes it easy to plug yourself in.
In my own country (New Zealand) when travelling I try to find places that are small (less than a few thousand population), perhaps without any accomodation (a sign of being a tourist destination). One great advantage of going to small towns overseas is that they are safe. Tourist cities are the most unsafe places I have travelled to (I particularly had unsafe situations in Rio and Nha Trang).
Perhaps apply your restaurant thinking, but just go a lot lot further down that path?
In many countries, I have felt like a millionaire, because the difference in income and situation is so profound. In Vietnam I remember talking with someone who’s monthly salary was USD50. I have met many people who had a disposable income of a few dollars a month. USD50 is less than my daily budget which is pure disposable money and is relatively obscene wealth (cost of flights alone exceeded USD50 per day: flights are expensive from New Zealand). I was just tooling around, like some sort of rich playboy, with no cares because I had been given everything by my country. I also remember how small many people were, because their food intake was limited by their means. I have very little capacity to relate, because I have never been in similar shoes (I do remember being astonished at the casual wealth of some Japanese and Americans when I was younger, but I haven’t lacked for anything in my life so it is entirely different).
I notice the same dynamic at home: my income as a software dev is radically different from many people I know. My disposable income is ridiculous: one acquaintance worked 40hours a week and was left with $20 to spend on themselves after expenses. I struggle to relate with a profit of 50 cents per hour.