Outlook broken on Firefox for 6 months – MS recommend switch to Edge

I don't quite know what their target audience is, but from my experience businesses (on desktop) primarily use Chromium based browsers, with a few percent of Safari users.

From business perspective, it can be quite reasonable to treat Safari bugs as low-ish priority, and just not dedicate any time to ensure other browsers work correctly. Of course this changes if you also need to support mobile/tablet devices, where iOS/Safari is similarly popular (if not more, depending on the location of your users) to Android/Chromium.

However, they should definitely update documentation, if they don't intent to keep FF support.