Anyone with a concern for keeping their data local or private, Nextcloud is a great solution.  They have come a long way since they forked from ownCloud.  Recently, I updated my installation to version 14.  Afterwards, I had to update a few database indexes (see below) and then came across a security warning.

chmod +x /var/www/nextcloud/occ
sudo -u www-data /var/www/nextcloud/occ db:add-missing-indices

Start of the security warning after updating:

The "Referrer-Policy" HTTP header is not set to "no-referrer", "no-referrer-when-downgrade", "strict-origin" or "strict-origin-when-cross-origin".

For now, I went with the strictest solution.  Afterwards, I noticed a complementary security scanner from Nextcloud (external scan, them scanning you).  I was happy to have received an A+!

If you have Nextcloud, give the scan a try!