On FreeBSD the config is located in "/usr/local/www/nextcloud/config/config.php", I'm unsure about Linux I haven't set it up for that. But, in the config you will see a marker for "trusted domains," I've set mine up for local DNS, zero-tier and local IP setup and it looks like this:

`'trusted_domains' =>

array (

0 => 'fileserver.home.lan:9000',

1 => '192.168.50.30:9000',

2 => '10.144.117.148:9000',

3 => '10.1.1.7',

4 => 'fileserver.home.lan',

5 => '192.168.50.30',

), `

Edit: You can see here more info on the config file. Per that documentation on Linux it should be under "/var/www/nextcloud/config/config.php"

Also of note, for internal IP addresses you should set the server to a static IP on your router, that's how I know my server will always be 192.168.50.30. If you're using home internet (not a VPS or business line) you're pretty much guaranteed to have a dynamic IP for public facing connections. For that I like noip.com because they have an app that will auto-update this so you can use the free domain name without needing to know the IP address that will change every few days. Duckdns also does this if memory serves though I think they just had a bash script you ran for this.