I discovered this article a while ago:

Avoiding Sexism in Legal Writing—The Pronoun Problem

https://lawyerist.com/49433/avoiding-sexism-in-legal-writing...

It has some solid advice, but it also notes that the use of "he" in sex-indeterminate situations was codified by Ann Fisher, "an 18th-Century schoolteacher and the first woman to write an English grammar book." Now, every time I see "he," I think of her.