You can access emails in a shared mailbox for which you have permission through the full Outlook client or online via the Office 365 web portal. For further information, please refer to the Microsoft support article on how to open and use a shared mailbox in Outlook.
https://support.microsoft.com/en-us/office/open-and-use-a-shared-mailbox-in-outlook-d94a8e9e-21f1-4240-808b-de9c9c088afd#OfficeVersion=Classic_Outlook
For Outlook on the web visit the following Microsoft support URL below:
https://support.microsoft.com/en-us/office/open-and-use-a-shared-mailbox-in-outlook-on-the-web-98b5a90d-4e38-415d-a030-f09a4cd28207