So I posted it.
It happened to me twice this morning.
In my first thought, I said, "What?"
On my second attempt, I still got the same error.
And I said to myself, "What the f*?"
Then, finally I found that in my appSettings.json, I misspelled the ConnectionStrings to ConnectionString.
Now, I realize that too much coffee is not a replacement to lack of sleep and not an excuse for stupidity, lol!
Anyway, I'm just having fun working on my dotNet Core project 😁