"Is this Action Group used by any alerts?"

If you want to find out if an Action Group is used by any alerts (metric or Log) how do you do it?

Two simple queries help here:

To check if any Metric alerts point to your Action Group, run

Get-AzMetricAlertRuleV2 | ?{$_.actions.ActionGroupId -like 'YourActionGroupName'}

To check if any Log Alerts (Known as Scheduled Query alerts since classic was retired) run

Get-AzScheduledQueryRule | ?{$_.action.aznsaction.actiongroup -like ''YourActionGroupName'}

Now you know if the Action Group is being used, and can be safely removed.