Hello Mir Hussain,
Thanks for your question
Sometimes, the Azure Portal may not reflect the latest changes immediately. Use the Azure CLI to check the disk status and attachment. You can use the following command to list the disks attached to the VM:
az vm disk list --resource-group <ResourceGroupName> --vm-name <VMName>
See reference issue: https://learn.microsoft.com/en-au/answers/questions/2133801/unable-to-manage-additional-disk-on-azure-vm
If this is not the case, create a technical ticket. See:
How to Create an Azure support request Create a support ticket
You can mark it 'Accept Answer' and 'Upvote' if this helped you
Regards,
Abiola