I get the confusion, Prabin Acharya.
You're right about Copilot being available for M365 Personal plan. However, Microsoft also notes that it is still rolling out, and not all features are available to all users everywhere. You can check the info from the FAQ here: Frequently asked questions about Copilot in OneDrive.
Since you have the supposedly correct plan and Copilot works in other services, this may simply mean that the OneDrive Copilot has not yet added to your account. So changing your primary alias should therefore not be necessary to qualify for this experience. Once it is available, you should see an option similar to this:
However, if it remains unavailable for a long time or you would like to utilize it as soon as possible, you will need some subscription / account side inspection. And since Microsoft Q&A is just a user-to-user support forum, contributors do not have access to back-end resources, it'd be best to contact the support team:
- Sign in with your account at Contact Us - Microsoft Support
- Enter / choose an issue > click Get Help to make a request
- Scroll down > Contact Support (if the option is available):
- Or click Ask our Support Assistant instead and follow guidance
- If the issue persists, specifically state in the chat box that you need direct help.
- The Contact Support button should appear now > click it > select the chat in browser option.
Note: The support contact team only works at certain times, so if the last window shows that it's unavailable, try opening it again the next day. If you prefer phone support, you can leave a phone number. This way, they can call you and help you.
I wish I could help further, but licensing/entitlement issues often involve personal account information. Those private details cannot and should not be reviewed on such a public platform.