I found an article on third cousins that may interest you.
Decades ago Mel Brooks and Carl Reiner came up with a skit about a 2,000 year old man. I can’t match that, but I did get notified today about a living relative, who according to his family tree is more than 200 years old. Supposedly he’s a descendant of one of my ancestors’ 3rd cousins. His data was matching mine in the late 1600s and everything was looking good until I got into the 1700s. There I encountered a man born in 1742, who he claimed was his living father. Chances are that a whole bunch of generations somehow got deleted from that branch of the tree he posted.
That got me thinking about something I once read about how its possible that DNA tests may not show a match with someone who is our 4th cousin. So I tried researchng that and encountered this article that may interest many of you. It has a lot of info on cousins and matching. See https://www.genealogyexplained.com/what-is-a-third-cousin/