Hi @Akash 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 enable the Microsoft Defender for Containers plan for Azure Arc AKS Clusters and could not find the option for Defender Plans to enable the plan in the Azure portal under Settings.
Solution:
The issue resolved itself and you were able to locate the plan. Note that you need to have an active subscription on the tenant in order to enable the plan.
If I missed anything please let me know and I'd be happy to add it to my answer, or feel free to comment below with any additional information.
If you have any other questions or are still running into more issues, please let me know. Thank you again for your time and patience throughout this issue.