Hi, last post, I've had it with this now (but it is solved for me so I post my fix here)...
I thought i'd uninstall, but uninstall postgresql wiped out half my installation because of "dependants", so I ended up reinstalling the whole damn OS.
I then had to do a from scratch Owncloud installation (my notes here)
Owncloud installation
sudo -i
dnf install postgresql nginx owncloud-nginx owncloud-postgresql owncloud-client-nautilus
# copy nginx.conf file and Letsencrypt certs from backup
systemctl enable --now nginx php-fpm
postgresql-setup initdb
systemctl enable --now postgresql
setsebool -P httpd_can_network_connect_db on
su - -c "psql" postgres
CREATE USER finite9 WITH PASSWORD 'secret password';
CREATE DATABASE owncloud TEMPLATE template0 ENCODING 'UNICODE';
ALTER DATABASE owncloud OWNER TO finite9;
GRANT ALL PRIVILEGES ON DATABASE owncloud TO finite9;
\password postgres
vi /var/lib/pgsql/data/pg_hba.conf
host all all localhost trust
vi /var/lib/pgsql/data/postgresql.conf
uncomment listen_address and port
vi /etc/owncloud/forcessl.config.php
<?php
$CONFIG = array (
'forcessl' => true,
);
Vi /etc/owncloud/config.php
# add the following
1 => 'myserver.nerdpol.ovh',
2 => '192.168.1.109',
# now set selinux context permissions as root
semanage fcontext -a -t httpd_sys_rw_content_t '/var/lib/owncloud/data(/.*)?'
semanage fcontext -a -t httpd_sys_rw_content_t '/var/lib/owncloud/config(/.*)?'
semanage fcontext -a -t httpd_sys_rw_content_t '/var/lib/owncloud/apps(/.*)?'
semanage fcontext -a -t httpd_sys_rw_content_t '/var/lib/owncloud/assets(/.*)?'
semanage fcontext -a -t httpd_sys_rw_content_t '/var/lib/owncloud/.htaccess'
semanage fcontext -a -t httpd_sys_rw_content_t '/var/lib/owncloud/.user.ini'
restorecon -Rv '/var/lib/owncloud/'
# enable owncloud updates via web interface, but disable after use
setsebool httpd_unified on
# navigate to localhost/owncloud to run the setup wizard
# note that this needs to be done on the non-ssl version of the page on localhost
# note that for this to work, pg_hba.conf MUST use address "localhost" and not 127.0.0.1/32
Once the setup wizard has created the ocadm user , and BEFORE logging in, reset pg_hba.conf to:
local all all peer
# IPv4 local connections:
host all all localhost trust
# IPv6 local connections:
host all all ::1/128 ident
Turn on forcessl and edit the owncloud.conf file in /etc/owncloud
edit the host firewall and allow http and https
then restart nginx and postgresql and re-connect to the web interface using the https public address, not "localhost"
then I had to re-enable to contacts and calendar app in Owncloud. I thought at this point that maybe I should have tried just uninstalling the apps within OC instead, then re-adding them, in case the app itself was outdated for that newer version of owncloud.
Then I re-imported my saved contacts and calendar, tested contacts bi-directionally and they still work, added calDAV address in iPhone and guess what.... I'd been typing the god damn wrong address. "PRINCIPLES" is an English word which came naturally to me, whereas the correct, for Owncloud "PRINCIPALS" in the address was not natural for me. When i used principals, iPhone said it was all good and calendar now syncs in iPhone. I wonder if this was my problem all along 
correct address is https://myserver.com/owncloud/remote.php/dav/principals/users/myuser/ This url is listed in the web interface of the calendar under the settings icon.
Hope some of this helps you in case you have different issue. By the way, all of that rewrite rule stuff was completely unnecessary for me, even when not having OC in webroot.
