"Table for one" is nearly always accommodated. Bringing a family of 4 or 5 out, and you're much more likely to be denied, or to suffer a long wait.

And, in fact, if there's a bar where they serve food that makes it even easier.

This is extremely uncommon in my experience, to the point where I've really only heard of it happening secondhand. I've seen people eating alone everywhere from fast food to Michelin star restaurants and done it myself many times. Where have you seen it?

In my experience as well, never been denied dining. But... maybe different parts of the world have different customs.

I’ve eaten alone in hundreds of places in dozens of countries, not sure where these mythical places are.

I mean, you almost always can? During COVID, there was a certain degree of reservations required--min 2 people. But it's pretty darned rare. And I say this as someone who has eaten out solo many hundreds of times. (And tend to eat at fairly decent restaurants.)