Hey @DarDarSara,
My suggestion is to start using Microsoft 365 Activities. These fully support Shared Mailbox functionality.
I would discourage building new Automations with Outlook activities as Microsoft introduced the New Outlook which doesn’t work anymore with Outlook Activities. They will push in the following years more aggressively for companies to move to the new Outlook.
I leave you some references.
New Outlook: Guide to product availability - Microsoft 365 Apps | Microsoft Learn