Hello everyone!
I have noticed quite several queries on the make.com community about whether it is even possible to use M365 Shared mailboxes in your Make.com scenarios:
Microsoft 365 Shared Mailbox - Questions & Answers - Make Community
and
Microsoft 365 Email / Watch Messages / Shared Mailbox - Questions & Answers - Make Community
All of them have been closed without Solving, so I decided to start a new thread and explain how you can do this for your projects.
The problem: When users try to create a connection and add an M365 shared mailbox to their scenario, they get redirected to the Microsoft login page. If they simply try to
sign in using their shared mailbox email address they will get an error and a connection will never be created.
Solution: To solve this issue you need to be an administrator in your Microsoft 365 account. If you are an administrator simply navigate to https://admin.microsoft.com/. Then using the left pane menu proceed to Users > Active users > Choose the shared mailbox you wish to connect to your Make.com scenario. On the top right corner click “Reset password” (read - Set password as you have never set a password for your Shared mailbox before).
After you reset(/set) the password, return to the Make.com scenario page. Now you can add a connection and sign in to Shared Mailbox using the Email address and Password that you have just set on Microsoft 365 Admin Page. The procedure itself is the same as if you connect your personal Email address. 
P.S. Maybe the M365 will also ask you to install their Authenticator app and log in with a Shared email account. The procedure itself is quite simple.
P.S. 2. Please note that you will require this password to create a Make.com connection only. You will not need that password to log into the Outlook application.
