Bizarrely, one cannot make OR queries in Microsoft Outlook for Mac, at least not easily.
For example, I want a smart folder that contains all messages tagged with either the FIS Broker category or the Dubletten category.
The way to do it non-easily is to select Raw Query as the query rule type (in Search > Advanced), and then enter a Spotlight query string.
The attribute to query for categories is com_microsoft_outlook_categories.
That attribute takes a numeric id - but what the hell is the id for a category like FIS Broker?
Outlook doesn't tell me, so I have to go even deeper down the rabbit hole.
Here is how: