Hi @Tarun Sharma ,
I'm glad that you were able to resolve your issue and thank you for posting your solution so that others experiencing the same thing can easily reference this! Since the Microsoft Q&A community has a policy that "The question author cannot accept their own answer. They can only accept answers by others ", I'll repost your solution in case you'd like to "Accept " the answer.
Issue:
You were trying to connect your Azure Devops account to Defender for Cloud using the Azure DevOps connection settings. You correctly authorized Defender to connect to your ADO account. However, you couldn't find your ADO Org to connect after authorization in Azure.
Solution:
Your ADO organization was located in the Microsoft Directory. When you created your organization and projects in the default directory they appeared correctly to be selected in the Defender for Cloud Devops connector.
Please remember to "Accept Answer" if any answer/reply helped, so that others in the community facing similar issues can easily find the solution.