Why Power Automate flow is not running from the SharePoint list?
When you create flow from the flow editor in PowerApps, by default the flow is an instance flow that has a PowerApps trigger that will run successfully from the context of PowerApps and this explains why your flow runs successfully while customizing the form in PowerApps.
But after publishing the form, it will run from SharePoint so its parent now is SharePoint, not PowerApps So the PowerApps trigger does not fire, as it sees Share point,
Solution:
You have to create either an Automated flow or delete the PowerApps trigger and add a manual trigger flow to avoid this issue.