I am definitely on team revise-to-avoid-using-“they”-as-a-singular-pronoun, but the 2017 edition of the AP Stylebook (the industry standard writing guide for journalists) acknowledges the limited use of “they” as a singular pronoun.
As always, the goal is clarity, not rigid adherence to a rule.
They/them/their is acceptable in limited cases as a singular and-or gender-neutral pronoun, when alternative wording is overly awkward or clumsy. However, rewording usually is possible and always is preferable. Clarity is a top priority; gender-neutral use of a singular they is unfamiliar to many readers. —AP Definitive Source