Following your link I found https://github.com/owncloud/calendar/issues/1002 and the second comment has a solution that fixes the problem for me. I did a vimdiff on his file and without understanding much I can tell you that the changes look reasonable. I have only been testing for 5 minutes but so far it works.
Doesn't regocnize Open Tasks preinstalled with /e/ foundation
Running /e/ on a Nexus 5x (bullhead) DAVx⁵ keeps saying that Open Tasks is not installed. But in /e/ this is a system app (foundation.e.tasks). Probably DAVx⁵ just does not have the permission to list those apps (see also "Open Tasks not installed"… although it actually is).
Does anyone know how this can be granted? The android is nougat.
The permission is hardcoded to the “dmfs.org.tasks” package name, if the package was re-branded under a different name this won’t work. It must be the exact name otherwise a sync of tasks into the Open Tasks storage will not be possible.
Thank you @devvv4ever for the quick reply!
In fact, I just found that DAVx⁵ is integrated into /e/ anyway. You just have to create a new WebDAV account in
Settings → Users & Account → Add account.
So tasks works with the pre-installed version of DAVx5 and the taskls app on /e/?
Yes, working perfectly!