More people may also be watching in delayed viewing far later than in prior seasons, potentially because there’s something else they’d rather be watching live around that time.
While The Big Bang Theory’s end is a factor, it’s not like this drop in viewership can be squarely attributed to it neccesarily.
Young Sheldon exists in an era where cord-cutting is increasingly on the rise, as part of the golden age of television we live in.
There are multiple factors that could be at play here.