Thailand has private rooms at dorm prices and street food where nobody notices a solo diner, which removes both solo penalties at once.
Portugal is compact, cheap and connected by buses, which makes it one of the easiest European countries alone.
New Zealand's solo travel works because the whole country moves along one circuit in the same direction.
Japan has restaurant formats, hotel categories and social conventions designed around people doing things by themselves.
Solo-friendliness is a set of specific infrastructure features rather than a general feeling about a place.
Solo travel safety is mostly unglamorous habits rather than gadgets or destination choices.
The hardest part of solo travel for most people is not safety or logistics but sitting down to dinner by yourself.