They is overwhelmingly used for plural. See how the wikipedia article starts:
> They is the third-person plural personal pronoun (subjective case) in Modern English.
And only after that:
> Although still controversial,[citation needed] and not officially accepted in formal context,[citation needed] it is also used with singular meaning, sometimes to avoid specifying the gender of the person referred to: see gender neutrality in language.
> They is the third-person plural personal pronoun (subjective case) in Modern English.
And only after that:
> Although still controversial,[citation needed] and not officially accepted in formal context,[citation needed] it is also used with singular meaning, sometimes to avoid specifying the gender of the person referred to: see gender neutrality in language.
https://en.wikipedia.org/wiki/They