When using:
snap install nextcloud
snap connect nextcloud:removable-media
sudo nextcloud.enable-https self-signed
How do I make sure that my Webserver is only accessible from inside my LAN? I dont want nextcloud open to anything else except my verizon local router network at home. Do you guys know how to do this?
Consider how your network and the internet is structured. Your computers are behind your router, which has an IP address from your ISP. Your router hands out its own IPs to your computers, and NATs traffic to/from the public IP.
The only way for your computer to be accessible (or not) beyond your router is a setting on your router: forward ports 80 and 443 to the computer hosting nextcloud if you want it accessible from outside your network, and don't do so if you don't want it to be accessible.
By default, your Nextcloud install will only be available on your local network unless for some reason you already have the aforementioned forwarding rules in place.