I reached out to the owner of this domain, and they very graciously allowed me to take it over:
Me: "Hi presumably fellow Nathan,
I was wondering if you would be kind enough to allow me to use nathan.is-a.dev as I see you created nathan.json in that repo. https://github.com/is-a-dev/register/blob/main/domains/nathan.json As a fellow Nathan and fellow dev, the domain I was using previously is getting a bit too expensive, so would greatly greatly appreciate it, if you wouldn't mind? Only reaching out because it seems like the domain is not used currently? If I am wrong, no worries, but I thought it was worth asking.
Best,
Another Nathan"
Them: "Yes of course you can use it. I bought my own domain name a long time ago so no worries there, i’m not sure how the process of giving you the domain goes but you have my approval, lmk of anything else i need to do to help you out 👍
Yours truly,
The other Nathan in question"