Using Classic Outlook on Windows for personal email, calendar, and contact management
Latest from Office 365 Roadmap page shows the feature has changed and slipped, now looking at September / October
So on the roadmap is both adding shared mailboxes as accounts (at which point you can favourite a folder) and specifically adding a shared folder to Favourites. Former in now Sept / Oct, latter is now July / Aug.
Long time getting here but is on its way.
Also, an observation for those complaining about the new outlook mine updated and I no longer had the toggle to switch back, but in reality it had installed a separate instance
I now have both old and new outlook installed (and both can be run at the same time)