Not entirely. For many centuries singular ‘they’ had been used when gender is uncertain or unknown. In the last hundred years or so some (primarily American) l

Not entirely. For many centuries singular ‘they’ had been used when gender is uncertain or unknown. In the last hundred years or so some (primarily American) language teachers decided that singular ‘they’ was wrong and adopted ‘he/she’. See https://public.oed.com/blog/a-brief-history-of-singular-they/ https://public.oed.com/blog/a-brief-history-of-singular-they... for a history.