https://screenrant.com/young-sheldon-season-7-coopers-big-bang-theory-finale-absence-explained/

As Sheldon decides where to go for his post-grad in Young Sheldon, it makes it clear why the Coopers didn't appear in The Big Bang Theory finale.

Young Sheldon Season 7 Set Up A Recurring Big Bang Theory Plot By Ending A Major Story (https://screenrant.com/young-sheldon-season-7-sturgis-linkletter-hagemeyer-tbbt-future/)

Young Sheldon season 7 ended the title character's search for his next college and, in the process, set up a recurring gag from The Big Bang Theory.