Unless they changed it recently, you can’t. It’s ridiculous and an aggressive sales tactic to get more people using one drive so ms has direct access to user files, plus some even pay them for a subscription.

There’s workarounds, like addons can still trigger a save and it’s possible for outside tools to send ctrl+s signals periodically. But as far as I know (and a quick search doesn’t contradict this), current versions of ms office refuse to autosave local files.