A popup in a scheduled event? That has no use, because the SE is run in the background, so no screen is involved.
As a first assumption, you created a button that calls MyFirstModule.Alert_3 and only modeled that to call a microflow.
If so: a button click that is modeled to execute a microflow does give not pop-up, unless you configure it in the button properties under microflow settings. You can configure a confirm prompt here which will throw a pop-up.
This microflow is also used in a scheduled event, so my second assumption is there is no page involved. This means you will by definition not see anything during execution (except console logging if you modeled that in your flow). To keep track of when it is finished executing, use the same microflow settings option and configure the progress bar of the button. By blocking the screen and providing a progress message you will have a visual indication of the execution.
There is a lot more to tell (best practices & experience) but these are modeling basics to start with.