I can connect to my NAS server (omv 5 nas) and i can use the app when on my local network wifi, but not on any other wifi or my 4g, ive read that i could need a DNS, if this is the case how do i go about adding a dns and what dns should i use? thanks
There should not be any difference to connect using the app or a separate computer.
You need to make sure that you can connect via your external IP (find it out here for example: https://www.whatsmyip.org). Then you need to enable port-forwarding (or port mapping) in your router on port 80 (http) and 443 (https) to the ip of your server. That is, when you access your external IP 1.2.3.4 it will forward it to your nextcloud server on address 192.168.0.100 (for example). It is a good idea to have static ip for your nextcloud server.
When that works you can get a domain name, for example I use https://www.noip.com to get a hostname, then you can connect using a name instead of the ip number.
This may lead to a problem that you cannot connect to the server when you are on your own wifi (on the inside). Then you need to setup DNS server. I cannot remember right now how I did it, but I will try to help when you can access your Nextcloud server from the outside.
i found the problem was with the DNS, i can access on my own wifi but not off my wifi, although it works on web browser on my phone using 4g so i figured it was just that the app on my phone wasnt loading the DNS information or something, i just got rid of the app and use the browser on my phone instead. i used duck dns