I installed Nextcloud on my home server within my domain folder and cannot access it from the outside

Nextcloud version _14
Operating system and version _Ubuntu 16.04
Apache or nginx version Apache 2.4.25):
PHP version _7.0

The issue you are facing:

I have my home domain website set up at: www.domainname.com and I installed Nextcloud within that directory under a virtual server called /var/www/kimosabeit.com/nextcloud/

I can access the website no problem but I cannot access Nextcloud externally. Do I need to open up a port or something?

Are both domain DNS records and NC on the same server?
use this service to confirm that the domain it pointing to the server IP https://www.whatsmydns.net/

If it is, then are you using apache or nginx? i assume apache if the directory is (/var/www/), review your nextcloud.conf file, you might have missed something in there.