Why haven't I gotten an alert to upgrade Final Cut Pro to 10.4.9?

In the App store, go to the FCP-X page. Does the blue button in the upper right say Update?

If so, and you are properly prepared, then click it to update your software.

MtD

Hard to say...but here are the Release Notes. Before installing a Final Cut Pro X update, verify that your system still meets Final Cut Pro X system requirements. Then make sure to back up your current version of the Final Cut Pro X application and your Final Cut Pro libraries.

Happy video editing, color grading, motion graphics manipulation n and all around post production fun!

JDee