Hi,
I've never encountered a Availability Zone quota limit nor have I seen it documented anywhere in Azure limitations. So if you are asking is there a quota limit to the number of VMs that may be created in a specific (e.g. Zone 2) Availability Zone I would say the answer is No.
Please note there is a Total Regional vCPUs quota for each Azure region, but that isn't specifically related to Availability Zones.
What I have encountered is when you attempt to start a vm, and/or scale out and/or scale up the request may fail due to a capacity issue. This is separate from a VM quota limitation whereby you could normally simply request an increase in relevant quota.
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Thanks.
-TP