i had the same problem with a samsung S4 (GT i9515) running lineage OS (lineage-17.1-20200926-nightly-jfvelte-signed) and the latest davx5 from F-Droid (v. 3.3.2-ose).
the slider to set the
Task rights was set to
granted. The debug info showed the
the problem appeared after a fresh install. still i tried to uninstall both OpenTasks and davx5 and change the install order, since i remember that this used to be a solution, did not work f or me though.
i had to use adb as described by @paultt
here is some additional information for others who want to use adb and don’t know how to use it (like me):
first install adb for your system, open a command prompt and then type
user@pcname:~$ adb devices
on your phone, allow your computer to access the phone via adb, then open an adb shell and send the command to set the permissions, like so
user@pcname:~$ adb -d shell
phonename:/ $ pm grant at.bitfire.davdroid org.dmfs.permission.READ_TASKS
phonename:/ $ pm grant at.bitfire.davdroid org.dmfs.permission.WRITE_TASKS
phonename:/ $ exit
i hope this helps.