I'm curious: why are people told not to use the em dash and the semicolon? I honestly don't know.

When I learned English writing, I was taught to use an em dash after words like 'by the way' or 'to add to that' — as a kind of aside. For hyphens, I was taught to use them in compound words. And for semicolons, I learned to use them when moving on to the next sentence within the same clause.

Actually, this is formal writing — techniques I learned in graduate school. Is this 'AI writing'?

It's hard because I'm not a native speaker.

He's not a native English speaker so I suspect he is heavily using AI to generate his comments and seems oblivious to how em dash is viewed in the anglosphere post-chatgpt