I know how to make repositories visible to everyone, but how do I make public repositories clonable by users that aren’t registered on my server?
If the repo is public anyone should be able to clone it via HTTP/HTTPS without any additional setup; assuming you don’t have another authentication system in front of gitea.
If you mean fork the repo in your instance, they can’t without being registered.
The repository is public, but peers can only
git clone when able to enter a username + a corresponding password.
Assuming they’re cloning using HTTP/S please be sure you’ve configured your site to provide the correct base url and port.
I assume it wouldn’t work at all, if they were incorrect.
It’s possible. For instance one could be using SSH and not have provided an ssh key to gitea. Or, they could have an ssh key set but the port mapping is wrong (i.e. 22 vs 2222). If the issue is the base url you could have a hosts file setting they don’t. It’s really hard to say without more detail.