Hi @Powerappsuser11 ,
Why don't you create a Automated MS Flow that triggers on a specific time of the day checking if any user hasn't logged in?
Instead trying to trigger the flow using Canvas App implies dependency for a User to trigger the Flow for notification.
But if you still want to do so, you can create 'PowerApps' trigger flow to trigger from the App.
You can pass parameters as you implement in the flow
To ask for parameter => In flow, simply scroll in dynamic content to find 'Ask in PowerApps' to show an argument needed in the App.
Once flow is executed, you can send the response back to PowerApps to show if Flow has failed or Executed successfully (optional)
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Now, you can either trigger flow for individual users or in bulk which is up to you.
Hope this helps