Instead of a file share, an immutable Blob storage is required.
Time-based retention policy support: Users can set policies to store data for a specified interval. When a time-based retention policy is set, blobs can be created and read, but not modified or deleted. After the retention period has expired, blobs can be deleted but not overwritten.
Note: Set retention policies and legal holds
1. Create a new container or select an existing container to store the blobs that need to be kept in the immutable state. The container must be in a general-purpose v2 or Blob storage account.
2. Select Access policy in the container settings. Then select Add policy under Immutable blob storage.
3. To enable time-based retention, select Time-based retention from the drop-down menu.
4. Enter the retention interval in days (acceptable values are 1 to 146000 days).
References:
https://docs.microsoft.com/en-us/azure/storage/blobs/storage-blob-immutable-storage
https://docs.microsoft.com/en-us/azure/storage/blobs/storage-blob-immutability-policies-manage