For those wondering about their add-ins, Microsoft quote “To provide a more reliable and stable add-in experience, VSTO and COM add-ins aren’t supported in the new Outlook on Windows. To ensure your add-in continues to work in the new Outlook on Windows, you must migrate your VSTO or COM add-in to an Outlook web add-in.”
Looks like it might be a while until businesses move to this web based version then, as many rely on business extensions in Outlook.