I had the same problem and @robertkwild 's solution worked (many thanks!)
However, like @vinc, I don’t have /etc/httpd/conf.d/ssl.conf so instead, I opened my /etc/apache2/sites-enabled/default-ssl.conf and added the two lines
Redirect 301 /.well-known/carddav /nextcloud/remote.php/dav
Redirect 301 /.well-known/caldav /nextcloud/remote.php/dav
below the <VirtualHost>...</VirtualHost> section (but above </IfModule>).
Although this works and I don’t get the warnings anymore, I don’t understand at all why it works. I would appreciate any hints why the lines work in this place and not in the nextcloud.conf or any .htaccess file in /var/www/html or /var/www/nextcloud like the documentation suggests…