If you setup Log Analytics for Azure Virtual Desktop, it should be possible to setup an alert or monitor for session hosts with 0 sessions for 14 days.
Create a Log Analytics query to check for Active Sessions. For example:
WVDConnections
| where TimeGenerated > ago(14d)
| summarize ActiveSessions = count() by
| where ActiveSessions == 0
This recent Q&A thread goes over a similar configuration. Please check to see if it helps. Let me know if you have any questions or run into any issues.
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