So, you need to:
Forward port 443 from the firewall (router) to 443 on the NC server (or 80 for non-SSL setups). Forwarding 80 TO 443 sounds like you've opened every port from 80 to 443. If that's not the case then great, but you only need one of those ports.
Next, it's now telling you that the only trusted domain you've added during installation is likely the internal IP address. For security it doesn't allow anyone to connect via any domain pointed at your server. It should have prompted you to add it automactically by logging in and clicking authorise, but if not, you can add it in your
config/config.php file located in the root of your NC installation (
In there you can find and edit so the lines read like:
0 => '192.168.1.100',
1 => 'cloud.domain.com',
Finally it's indicating you have a permissions issue, so you need to SSH back into your server and do a
sudo chmod -R 770 /var/www/html/nextcloud/data. Really it sounds like you might need to find the permissions guide on the NC docs to ensure you're not leaving anything else world-readable also.
Hope that helps