@Anant Bera, thanks for posting in Q&A. After going through your process. I find the device is only Autopilot register in new tenant. The device is not Autopilot enrolled into Intune. You can check the MDM of the device object in Microsoft Entra ID. It will show none. And the device object is not in Intune.
For existing using device, we need to do windows reset to trigger it to download the Autopilot enrollment profile to do the enroll. If you don't want to reset the device, you can choose other enrollment method instead of Autopilot enrollment method. Like configure Automatic enrollment and then do Microsoft Entra Join to trigger the device enroll into Intune.
Hope the above information can help.
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