We migrated earlier this year and had a similar problem. Outlook (classic) works differently than the OWA version. They keep the classic version so people don't spontaneously throw a chair out a window. It's being phased out slowly.
The macOS version still has all of them beat.
I don't use Outlook for my personal email, but I've used it in various corporate engagements and not been wholly dissatisfied. Newer versions are slower, more bloated, and unstable (though add-ins-- especially the Teams add-in-- contribute to that).
The most egregious regression, for me, has been the "Advanced Find" functionality (which was wonderful in the 97 thru 2010 versions) being changed-out for the god-awful search box within the Outlook window.
Considering this is a spacecraft, that explains everything.