How to log that a flow has been executed in Scheduler

The most appropriate method is to output logs using the Logger component in the flow's context.

Alternatively, you can enable logging by setting the following package to the DEBUG level.
<AsyncLogger name="org.mule.runtime.core.internal.context.notification.Policy" level="DEBUG"/>

The following log entries will be recorded.
“resourceId” is the name of the flow.

DEBUG 2025-04-10 18:09:03,627 [[MuleRuntime].uber.11: org.mule.runtime.core.internal.source.scheduler.DefaultSchedulerMessageSource.pollingExecutor - myfirstappFlow/source @2a834d0b] [processor: ; event: ] org.mule.runtime.core.internal.context.notification.Policy: Sending notification: PipelineMessageNotification{action=pipeline process start, resourceId=myfirstappFlow, serverId=shinyas-ltmwgp8.internal.salesforce.com..myfirstapp, timestamp=1744276143627}