Is it possible to unarchive repository one it is archived?

The GitHub documentation on archiving repositories does not mention if this is a one way operation or if let say I did archive the wrong repository my mistake or if I change my mind I can “un-archive” it and make is active again?

It’s reachable via /settings in the same place as you would have archived the repository:

Interesting that you mention a lack of documentation, there is documentation for restoring deleted repositories (you apparently have 90 days for isolated repositories – you can’t recover deleted forks in live networks – although you could probably retrieve the individual commits):
And this is linked from its sibling:

Ticket to document: Create documentation for unarchiving-repositories · Issue #18753 · github/docs · GitHub