Are folks still having the original issue? I’m not seeing the issue after updating PHP on my box, and there was a second update that may have resolved it (according to #102 - The FPM systemd unit has been hardened - oerdnj/deb.sury.org - Codeberg.org).
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.