Hi @Mital Shah ,
user y cannot access shared calendar of user x@domainA as the connect button is greyed out.
Would you mind sharing a screenshot of this after removing all personal information like email addresses? Since as I know, normally we can follow the instructions in this document to open a shared calendar and no "Connect" button is involved in the procedure:
If user y is using Outlook for Microsoft 365, the "Open Shared Calendar" button can be found via Home > Add calendar:
For your situation, please ensure that calendar of y@domainA is selected in the lower left pane when trying to add the shared calendar of user x@domainA.
If the issue persists or should I've misunderstood anything, feel free to let me know.
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