How to trigger task when Play/Pause button is pressed on Podcast Addict widget or notification?
You can't do it this way. Buttons on widgets are signalled via intents, that's true, but the intent is delivered only to the app that owns the widget - in this case, Podcast Addict.

Instead, you should create a button widget through Tasker, and have it trigger a profile which does the other stuff you want and sends the same intent to Podcast Addict that its own widget would send.