That's correct. 16.04 LTS is nearing end of life, expiring 5/20/2021, as shown in portal below:
The recommended replacement image to use is18.04 lts
You can also find VM images supported by Azure Batch service by using the command :
az batch pool supported-images list
It lists all Virtual Machine Images supported by the Azure Batch service.
az batch pool supported-images list [--account-endpoint]
[--account-key]
[--account-name]
[--filter]
[--query-examples]
[--subscription]
Hope that helps.
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