If there is one change that I hate the most it is the concept of gendered endings for both persons and titles. There is no such thing as "singular they", if you do not know the gender of the person that you're addressing, you should use "he" and the reason for that has to do with German:
In recent years (since about 1990/2000?) (((German teachers))) forced the endings of titles and job descriptions from pure-male into male / female form (you even get a fine if you don't do it, by German law, oy vey), then started telling everyone that titles / jobs being male was a result of patriarchy and the reason that "the worker" - "der Arbeiter" had no female "-in" ending was because women weren't allowed in the workforce. That is not the case: title, status and jobs used to be always male. I recently noticed it when they took it too far: "the customer" - "der Kunde", not "die Kundin", and especially the plural form "the customers" - "Die Kunden / die Kundinnen" - there is no such word as "Kundinnen", it's a bastardization of the German language. "Saying 'die Kunden' (the customers) would exclude women from being customers" - no it fucking doesn't. "Customer" is a status, a role. Roles always have male ending, end of story. "The teacher" - "der Lehrer", "the pupil" - "der Schüler": (((Germans))) have tried - and largely succeeded - to undermine this concept by saying that because of the male "-er" ending, it would not include women.
It's especially noticable in the German plural form where "-in" has to be extended to "-innen": "Die Schüler" (plural) - "die Schülerinnen": There is no such word, "Schüler" (pupils, plural) includes girls, too, because "Schüler" is a status. But teachers wouldn't have it.
Then they've even gone further by pushing a "diverse" form (male / female / diverse) and introducing it as an "inclusivity star", so now you have to write "Kund*innnen" or "KundInnen" to also include trans people of color - or else! It's an abomination of language and it happened fast enough that I can still remember everyone using "he" and male endings. For teaching spanish they've even tried to force pupils to write the "@" sign to designate "o/a" endings. Why, just why.
Right now they are forcing everyone to use "he/she" in conversations or "they" (as people get tired of a change that wasn't there originally). Job descriptions and titles (such as "the user" - "der Nutzer") used to be male, there was no female "the user-in" - "die Nutzer-in" form. "She is a worker", not "she is a worker-in". Only in recent years some (((people))) have started forcing using gendered endings for titles, jobs, and roles and we should resist it in our own conversations.
The reason "singular they" is deranged is understandable to anyone with two braincells: Because then there is no distinguishable form between singular and plural. "They gave me some apples" - he or she, singular or plural? German has "Sie" or "usted" in Spanish as the polite, non-gendered version of addressing someone. English has no such thing. You are talking to a person as if he has multiple personalities and I think that's what they want.
Your language is an expression of your feelings. If you can't express a concept - in this case masculinity for titles - then it doesn't exist. That is why want to subvert language, to control your feelings, your emotions, and to turn non-political concepts into political ones, in order to further divide people.