I don’t think ReadWritePaths=/usr/local/lib/owncloud is the right answer and I am surprised that solved it. Nextcloud is configured to use a different directory for data:
'datadirectory' => '/home/user-data/owncloud',
I’m not sure about what appstoreenabled is doing in this case.
i’m still having this issue on v75. Without appstoreenabled => false, i am unable to login to nextcloud or connect calendars over caldav. i’m not sure if it’s also related, but i also lost the ability to connect my iOS device to the Exchange endpoint as well (it kept prompting for my password - just like the caldav issue above)
As I am writing this after you have posted an updated version, this comment is likely not of immediate use. However, for future reference:
On my install, there is a link from: /usr/local/lib/owncloud/config/config.php to /home/user-data/owncloud/config.php. Maybe this is why the ReadWritePaths=/usr/local/lib/owncloud permission was required?