Consider the following sentence.
This sentence seems all right to me. However, when fed it to https://languagetool.org/, an online grammar checker, it complained about a missing comma before “so”. Did the online grammar checker make a mistake?
Your hunch is right: the online grammar checker is wrong. You don’t need a comma here. It’s helpful to remember so can mean and so or so that. When it means and so and joins two independent clauses, a comma is generally considered necessary. For example, Programmers can write efficient and type-safe code, [and] so good ones are in high demand. But in your sentence, so means so that — which does not need a comma. Grammar checkers often make this error, in my experience.