Use case difference between Deck and Tasks
I started using Nextcloud a few weeks ago as a home user. Succesfully I was also able to synchronize with Thunderbird for agenda and tasks as well as with my Android Fairphone 4 using cal/dav with DAVx5. But I realized that tasks in Deck are coming through well on Thunderbird as well as on Android, but when I am updating a task of a Deck list or creating a new task in a Deck list in Thunderbird or Android it does not flow back to Nextcloud. So I decided to ony use the Tasks app which synchronizes well in both directions.
But still I am wondering what the essential difference between the two is and why the Deck tasks are not syncing in both ways.
Maybe this is a bit a dummy question but searching the documentation did not bring me an answer - maybe looking in the wrong place.
Any help would be wonderful 
Some or all of the below information will be requested if it isn’t supplied; for fastest response please provide as much as you can. 
The Basics
- Nextcloud Server version (e.g., 29.x.x): no idea, I am using it with a provider Tab Digital
- Operating system and version (e.g., Ubuntu 24.04):
Linux Mint Virginia