A relative tells me he runs Owncloud instead of Nextcloud because Nextcloud can not be set up to run without a working connection to the internet. I believe the issue is with LetsEncrypt.
Basically he wants to use Nextcloud such that it can not be accessed from outside his house network.
you definitely can use Nextcloud without exposing it to the internet. the system itself requires internet access to install apps and updates (not really air-gapped) but incoming access is not a requirement. you simply don’t add port forwarding. this breaks things like TLS from letsencrypt but technically it works.
Before posting I looked around and found articles about how to deal with LetsEncrypt. From those articles it seems you have to update the keys manually every three months, which is why he said no to Nextcloud.
For some reason owncloud does not have such an issue. My relative’s claim is that owncloud lets you opt out of LetsEncrypt type authentication. Seemed odd which I why I was asking about it.
Q: "A relative tells me he runs Owncloud instead of Nextcloud because Nextcloud can not be set up to run without a working connection to the internet. "
A: No, your relative is wrong. We have multiple Nextcloud installations at customer sites (manufacturing) that hapilly live with no internet connectivity whatsoever.
Q: “I believe the issue is with LetsEncrypt.”
A: This is not a church. Beliefs do not matter here. Letsencrypt is one of the mechanisms to get TLS certificates. For non-internet connected applications, one of your possibilities is to create your own self-signed certificates. This is same for any web application, nothing to do with Nextcloud/Owncloud.
Q: “Basically he wants to use Nextcloud such that it can not be accessed from outside his house network.”
A: This is perfectly possible. The relative can just run it in the local network, no need to expose it to the outside internet.
Q: “I would think that was possible. Is it not?”
A: As per previous, this is perfectly possible and many folks aready do this.
Your questions are more related to general network, TLS, how to host any web application in a self-contained local network environment - principles are same, regardless of whether it is Nextcloud, Owncloud or anything else.
Perhaps you are unfamiliar with the use of “believe” in the sense of “I am unsure of the exact situation because I have only heard about it from another person”. Rein it in a bit cowboy.
This question was to clear up my opinion that a person could certainly do what he wanted with Nextcloud as well as owncloud.