Microsoft 365 features that help users manage their subscriptions, account settings, and billing information.
Hi mahdiidriss,
According to your description, my understanding is that after you created a new user mailbox and assigned the valid license to the user, you didn’t see the option “ convert to shared mailbox “ in the Office 365 Admin Center > Active User > Mail settings. For your reference Convert a user mailbox to a shared mailbox. However, you can use the option “ convert” in the EAC to convert it. Please clarify if I misunderstand your text.
As far as I know, for a new created user mailbox, it may need some time to prepare the mailbox settings ( including convert to shared mailbox). So if you didn’t see the option “ convert to shared mailbox” in the Office 365 Admin Center, please wait for some time and then refresh your browser page to check if you could see it.
If you have any other concern, welcome back to share with me, thanks.
Regards,
Oliver