Nov 09 2020
For bussiness accounts.
When you are creating an user in Micrsoft 365 and you share the mailbox to another user.
This other user can add the profile to outlook, but because it is also shared the mailbox, outlook 365 will crash when reopen again.
So add the mailbox and shared it also is not a good idea
Nov 10 2020
You can share the mailbox via PowerShell, and toggle off the -AutoMapping flag which causes it to appear automatically in Outlook.