K-9 is under development but a different individual. This is why the UI change and one of the changes is Tasker integration. At best it's broken, though I suspect the individual developing the app now doesn't value the integration. Basically it's currently developed to an individual's needs and shared and open source to the community. Which is fair, but it's going away from meeting my needs.
To get the integration back, you'll have to revert to 5.6 found on K-9's GitHub. It an APK under assets. If you do revert, don't forget to make sure you know the account password since on input of settings on the older version, you have to manual renter them. On the newer UI, the passwords are available in clear text if you go into server configuration and tap the eye icon. That's another feature I dislike in the new version.
An alternative is AquaMail which has Tasker integration.
Logcat can detect the total duration of and how far you are into a podcast on Podcast Addict. I haven't tried this with any other app but I assume that there's good chance that this profile could be adapted for other apps.
The profile pauses Podcast Addict at night and when there are less than 10 seconds remaining in the podcast.
Note: Logcat returns all durations in ms for Podcast Addict.
My current use case is to make it easier to finish podcasts in the morning since I go to sleep while listening to them. It's a pain to find episode 140/173 when it's marked as played, now I don't have to do that!