As a former English teacher who did take advanced grammar in college, I learned that grammarians don't always agree with each other on grammar issues. Now I’m learning that what once was considered proper grammar when I was in school is now controversial. Take the Oxford comma, for example.
And don’t get me started on Grammarly. It can find typos and simple usage mistakes I might miss, but it makes many suggestions that are just plain wrong. It could mislead the very people who rely on it for help. The best way to be correct is to learn grammar and usage yourself and use a good spellchecker to help you catch the errors you didn’t notice when you were proofreading.