I've been using double hyphens (which auto-corrects to emdash now) for as long as I can remember. Now that it's a marker of AI, I find myself removing it whenever I reply to comments.

I always used three hyphens in place of the emdash; easier to type.

While I've seen it in tooling like markdown--with two being an endash--that's very very wide... I am very sure the convention has always been to use two hyphens for an mdash (which is even easier to type! ;P).

Some of my acquaintances were doing the same, but unintentionally.

I had also thought news articles and the like were using regular hyphens that were extended due to some weird font.