>> The desktop outlook (the real one, not the 'new' one which is just the web version) is much better of course as it searches locally but it's only on windows.

I am very confused by the MicroSoft product branding, but on MacOS there is a "proper" application: "Microsoft Outlook for Mac". As I understand this is called the "New Outlook" which is a native, non-Electron version. As it is not Electron based it is only 2.6GB (/s).

Anyways.. the search capabilities are insanely bad for searches outside of your current mailbox. It might be related to handling of large result sets where it just provides a limited set of random hits as opposed to a set with the most recent hits. When you provide from-to dates (from a hideously complicated "advanced" menu) the results seem a bit better.

edit/addition: on MacOS, Outlook supposedly uses the native "Spotlight" search engine. MacOS spotlight, when used from the Finder, actually does a really good job in finding the E-mail .eml files from the file system and, when clicked, they open up in Outlook.