We've all struggled with teachers or professors marking papers wrong because we used a singular "they" instead of using an exclusionary "him/her." We've all had to sweat over how to reword a document, so that we do not even have to make that decision. The good news is, we no longer have to undergo that stress! The American Dialect Society selected "they" as word of the year under the definition: "they: gender-neutral singular pronoun for a known person, as a non-binary identifier."
This was a necessary change. I have argued with various professors about this very issue. Many people who are invested in academia claim that using "they" as a singular term breaks basic grammar rules and leads to less clear writing.
I wholeheartedly disagree with any professor, teacher, or grammar nut who holds that view. Using him/her is almost always less clear communication and non-inclusive language. If a writer is choosing to use the term "him/her" it applies they do not know which gender pronoun to use. If that is the case, they should be using a term that captures all gender possibilities, and there are definitely more than two. So, if the goal is effective and clear communication, "they" is a more accurate pronoun.
Further, if a writer uses "him/her" when they do not know which gender the subject is, they are contributing to a society that erases the identities of those who fall outside of traditional gender roles. Normalizing "him/her" as the primary pronoun for unknown genders leads to the perception that there are only two genders, which only perpetuates the damaging gender binary. This is hugely problematic for non-binary people.
Essentially, promoting "him/her" pronoun usage is prioritizing tradition over clear communication and inclusivity. We cannot cling to outdated grammar rules at the expense of communicating most effectively and we cannot perpetuate a culture that invalidates a large community of people.