Is there a way to mass apply an action within photoshop elements to multiple photos at the same time (v2019)?
Applying Actions to a batch of files is not currently supported in Photoshop Elements.
There are a few operations that can be applied to a batch of images using "Process Multiple Files" option in PSE. You can refer to this help guide for steps and supported funcationalities.: https://helpx.adobe.com/in/photoshop-elements/using/opening-files.html#process_multiple_files
. . . you can also batch process some corrections to multiple files using the ACR Editor or the Instant Fix tool in the Organizer.