For the ninth post I found a pretty useful blog post about .NET Core and ASP.NET Core documentation updates for the version 3.0. This post was written by Maxime Rouiller, a former MVP, who now works for Microsoft as a Microsoft Cloud Developer Advocate.
In this post he shows all the important updates related to version 3.0 structured by topic including the links to the updated documentations. There is definitely a lot of stuff he is mentioning and you should read:
BTW: I personally met Maxime during the MVP Summit back when he still was MVP. The first time I met him during the breakfast at the summit hotels. He asked the MVPs at the breakfast table to try to spell his name and I was one of them who tried to speak his name in French which was right. This guy is so cool and funny. It was a pleasure to meet him.