If there is a backup, where are they backuped? Is that backup publicly available? Is it documented anywhere?
If not, then yes, git clones on people’s computers are almost identical, but should probably be safe and have an official backup too. There are also a lot of repos in the organization that aren’t active anymore and could possibly not have clones.
Some of the openstreemtmap org repos are mirrored here (mostly for deployment purposes, as stated on the page): https://git.openstreetmap.org/
All discussions on openstreetmap-website issues and pull requests are mirrored on the rails-dev mailing list: The rails-dev Archives
Is there software that can make these types of backups? I’d be interested in running it.
Clarify: Specifically backing up the github issues + other metadata. Using gh cli + git clone it is easy enough to backup all git repos.
Google it. I think I saw quite a few.
Google it. I think I saw quite a few.
Aaaaah thanks. You asked the question, now I must do the work 
This appears to be the most popular open source tool: GitHub - josegonzalez/python-github-backup: backup a github user or organization
Github have a dedicated backup tool for on-prem Github Enterprise, but that is a totally different beast.
The reason why I said Google it is because there might be options you personally might like better than others and I wouldn’t want to provide a limited list of options that might not be the best since there are a lot of them.
By the way, the GitHub Arctic Code Vault backed up a number of these repositories as of right before the pandemic. This was just the Git repositories themselves, but GitHub is partnering with the Internet Archive and Software Heritage Foundation on more regular backups that include issues and their event timelines. Not to detract from the idea of maintaining a more practical in-house backup. 