Explanation:
Box 1: Monthly
Windows supports monthly node image version upgrades.
Box 2: Weekly
Linux supports weekly node image version upgrades.
Note: Azure Kubernetes Service patch and upgrade guidance
This section of the Azure Kubernetes Service (AKS) day-2 operations guide describes patching and upgrading strategies for AKS worker nodes and Kubernetes versions. As a cluster operator, you need to have a plan for keeping your clusters up to date and monitoring Kubernetes API changes and deprecations over time.
Reference:
https://learn.microsoft.com/en-us/azure/architecture/operator-guides/aks/aks-upgrade-practices