How do Lightning Explorers like 1ML register closed channels?
Every Chanel that us public is announced on the gossip protocol and in the channel announcement message linked to a funding transaction. What you can do (and what 1ml most likely does) is to save spent funding TX as close channels. As the gossip protocol will only forward channel announcement messages for open channels (those where the funding TX was not spent) it will be impossible to query your lightning node for closed channels from the past. You will only be able to collect this data for the future. Or you could crawl 1ml if their robots.txt allows this.